Water vapour (5)

I believe the answer is:
steam
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">water vapour</span>' is the definition.<br/ ><span class="explanation-format__explanation">(steam from boiling water)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for steam that I've seen before include "Kettle emission" , "Source of energy" , "comes with a hiss?" , "Gas formed by vaporizing water at 100?C" , "Energy (colloq.)" .)