$(function() {
  // Get the HTML in #hoverText - just a wrapper for convenience
  var $hoverText = $("#hoverText");

  // Replace all spans inside paragraphs with their text
  $("p span", $hoverText).each(function() {
    var $this = $(this);
    var text = $this.text(); // get span content
    $this.replaceWith(text); // replace all span with just content
  });

  // Wrap words in spans AND preserve the whitespace
  $("p", $hoverText).each(function() {
    var $this = $(this);
    var newText = $this.text().replace(/([\s])([^\s]+)/g, "$1<span>$2</span>");
    newText = newText.replace(/^([^\s]+)/g, "<span>$1</span>");
    $this.empty().append(newText);
  });

  // Demo - bind hover to each span
  $('#hoverText span').hover(
    function() { $(this).css('background-color', '#ffff66'); },
    function() { $(this).css('background-color', ''); }
  );
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<div id="hoverText">
  <p><span class="kinovar"><span id="selection_index3337" class="selection_index"></span>По f7-мъ часЁ твори1тъ сщ7eнникъ начaло съ кади1ломъ и3 со свэщeю, цrкимъ двeремъ tвeрзєннымъ, и3 поeтъ: Х</span>rт0съ воскRсе: <span class="kinovar">со 
стіхи2. И# по стісёхъ pал0мъ: Б</span>лгcви2 душE моS гDа: <span class="kinovar">И# є3ктеніA. Тaже каfjсма nбhчнаz.</span>
  </p>
</div>

$(function() {
  // Get the HTML in #hoverText - just a wrapper for convenience
  var $hoverText = $("#hoverText");

  // Get the full word the cursor is over regardless of span breaks
  function getFullWord(event) {
     var i, begin, end, range, textNode, offset;
    
    // Internet Explorer
    if (document.body.createTextRange) {
       try {
         range = document.body.createTextRange();
         range.moveToPoint(event.clientX, event.clientY);
         range.select();
         range = getTextRangeBoundaryPosition(range, true);
      
         textNode = range.node;
         offset = range.offset;
       } catch(e) {
         return ""; // Sigh, IE
       }
    }
    
    // Firefox, Safari
    // REF: https://developer.mozilla.org/en-US/docs/Web/API/Document/caretPositionFromPoint
    else if (document.caretPositionFromPoint) {
      range = document.caretPositionFromPoint(event.clientX, event.clientY);
      textNode = range.offsetNode;
      offset = range.offset;

      // Chrome
      // REF: https://developer.mozilla.org/en-US/docs/Web/API/document/caretRangeFromPoint
    } else if (document.caretRangeFromPoint) {
      range = document.caretRangeFromPoint(event.clientX, event.clientY);
      textNode = range.startContainer;
      offset = range.startOffset;
    }

    // Only act on text nodes
    if (!textNode || textNode.nodeType !== Node.TEXT_NODE) {
      return "";
    }

    var data = textNode.textContent;

    // Sometimes the offset can be at the 'length' of the data.
    // It might be a bug with this 'experimental' feature
    // Compensate for this below
    if (offset >= data.length) {
      offset = data.length - 1;
    }

    // Ignore the cursor on spaces - these aren't words
    if (isW(data[offset])) {
      return "";
    }

    // Scan behind the current character until whitespace is found, or beginning
    i = begin = end = offset;
    while (i > 0 && !isW(data[i - 1])) {
      i--;
    }
    begin = i;

    // Scan ahead of the current character until whitespace is found, or end
    i = offset;
    while (i < data.length - 1 && !isW(data[i + 1])) {
      i++;
    }
    end = i;

    // This is our temporary word
    var word = data.substring(begin, end + 1);

    // Demo only
    showBridge(null, null, null);

    // If at a node boundary, cross over and see what 
    // the next word is and check if this should be added to our temp word
    if (end === data.length - 1 || begin === 0) {

      var nextNode = getNextNode(textNode);
      var prevNode = getPrevNode(textNode);

      // Get the next node text
      if (end == data.length - 1 && nextNode) {
        var nextText = nextNode.textContent;

        // Demo only
        showBridge(word, nextText, null);

        // Add the letters from the next text block until a whitespace, or end
        i = 0;
        while (i < nextText.length && !isW(nextText[i])) {
          word += nextText[i++];
        }

      } else if (begin === 0 && prevNode) {
        // Get the previous node text
        var prevText = prevNode.textContent;

        // Demo only
        showBridge(word, null, prevText);

        // Add the letters from the next text block until a whitespace, or end
        i = prevText.length - 1;
        while (i >= 0 && !isW(prevText[i])) {
          word = prevText[i--] + word;
        }
      }
    }
    return word;
  }

  // Return the word the cursor is over
  $hoverText.mousemove(function(e) {
    var word = getFullWord(e);
    if (word !== "") {
      $("#result").text(word);
    }
  });
});

// Helper functions

// Whitespace checker
function isW(s) {
  return /[ \f\n\r\t\v\u00A0\u2028\u2029]/.test(s);
}

// Barrier nodes are BR, DIV, P, PRE, TD, TR, ... 
function isBarrierNode(node) {
  return node ? /^(BR|DIV|P|PRE|TD|TR|TABLE)$/i.test(node.nodeName) : true;
}

// Try to find the next adjacent node
function getNextNode(node) {
  var n = null;
  // Does this node have a sibling?
  if (node.nextSibling) {
    n = node.nextSibling;

    // Doe this node's container have a sibling?
  } else if (node.parentNode && node.parentNode.nextSibling) {
    n = node.parentNode.nextSibling;
  }
  return isBarrierNode(n) ? null : n;
}

// Try to find the prev adjacent node
function getPrevNode(node) {
  var n = null;

  // Does this node have a sibling?
  if (node.previousSibling) {
    n = node.previousSibling;

    // Doe this node's container have a sibling?
  } else if (node.parentNode && node.parentNode.previousSibling) {
    n = node.parentNode.previousSibling;
  }
  return isBarrierNode(n) ? null : n;
}

// REF: http://stackoverflow.com/questions/3127369/how-to-get-selected-textnode-in-contenteditable-div-in-ie
function getChildIndex(node) {
  var i = 0;
  while( (node = node.previousSibling) ) {
    i++;
  }
  return i;
}

// All this code just to make this work with IE, OTL
// REF: http://stackoverflow.com/questions/3127369/how-to-get-selected-textnode-in-contenteditable-div-in-ie
function getTextRangeBoundaryPosition(textRange, isStart) {
  var workingRange = textRange.duplicate();
  workingRange.collapse(isStart);
  var containerElement = workingRange.parentElement();
  var workingNode = document.createElement("span");
  var comparison, workingComparisonType = isStart ?
    "StartToStart" : "StartToEnd";

  var boundaryPosition, boundaryNode;

  // Move the working range through the container's children, starting at
  // the end and working backwards, until the working range reaches or goes
  // past the boundary we're interested in
  do {
    containerElement.insertBefore(workingNode, workingNode.previousSibling);
    workingRange.moveToElementText(workingNode);
  } while ( (comparison = workingRange.compareEndPoints(
    workingComparisonType, textRange)) > 0 && workingNode.previousSibling);

  // We've now reached or gone past the boundary of the text range we're
  // interested in so have identified the node we want
  boundaryNode = workingNode.nextSibling;
  if (comparison == -1 && boundaryNode) {
    // This must be a data node (text, comment, cdata) since we've overshot.
    // The working range is collapsed at the start of the node containing
    // the text range's boundary, so we move the end of the working range
    // to the boundary point and measure the length of its text to get
    // the boundary's offset within the node
    workingRange.setEndPoint(isStart ? "EndToStart" : "EndToEnd", textRange);

    boundaryPosition = {
      node: boundaryNode,
      offset: workingRange.text.length
    };
  } else {
    // We've hit the boundary exactly, so this must be an element
    boundaryPosition = {
      node: containerElement,
      offset: getChildIndex(workingNode)
    };
  }

  // Clean up
  workingNode.parentNode.removeChild(workingNode);

  return boundaryPosition;
}

// DEMO-ONLY code - this shows how the word is recombined across boundaries
function showBridge(word, nextText, prevText) {
  if (nextText) {
    $("#bridge").html("<span class=\"word\">" + word + "</span>  |  " + nextText.substring(0, 20) + "...").show();
  } else if (prevText) {
    $("#bridge").html("..." + prevText.substring(prevText.length - 20, prevText.length) + "  |  <span class=\"word\">" + word + "</span>").show();
  } else {
    $("#bridge").hide();
  }
}

.kinovar { color:red; font-size:20px;}.slavic { color: blue;}#result {top:10px;left:10px;}#bridge { top:10px; right:80px;}.floater { position: fixed; background-color:white; border:2px solid black; padding:4px;}.word { color:blue;}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script> <div id="bridge" class="floater"></div> <div id="result" class="floater"></div> <div id="hoverText"><p><span class="kinovar"><span id="selection_index3337" class="selection_index"></span>По f7-мъ часЁ твори1тъ сщ7eнникъ начaло съ кади1ломъ и3 со свэщeю, цrкимъ двeремъ tвeрзєннымъ, и3 поeтъ: Х</span>rт0съ воскRсе: <span class="kinovar">со стіхи2. И# по стісёхъ pал0мъ: Б</span>лгcви2 душE моS гDа: <span class="kinovar">И# є3ктеніA. Тaже каfjсма nбhчнаz.</span></p><div class="slavic"> <input value="Works around other tags!"><p><span id="selection_index3737" class="selection_index"></span>(л. рo7з њб.)</p><p><span class="kinovar"><span id="selection_index3738" class="selection_index"></span>Во вт0рникъ вeчера</span> </p><p><span class="kinovar"><span id="selection_index3739" class="selection_index"></span>tдaніе прaздника пaсхи.</span></p><p><span class="kinovar"><span id="selection_index3740" class="selection_index"></span>По f7-мъ часЁ твори1тъ сщ7eнникъ начaло съ кади1ломъ и3 со свэщeю, цrкимъ двeремъ tвeрзєннымъ, и3 поeтъ: Х</span>rт0съ воскRсе: <span class="kinovar">со стіхи2. И# по стісёхъ pал0мъ: Б</span>лгcви2 душE моS гDа: <span class="kinovar">И# є3ктеніA. Тaже каfjсма nбhчнаz.<input value="Works around inline tags too"></span></p><p><span class="kinovar"><span id="selection_index3741" class="selection_index"></span>На ГDи воззвaхъ: поeмъ стіхи6ры самоглaсны, слэпaгw, на ѕ7. Глaсъ в7:</span></p></div>