Krypton or xenon
I believe the answer is:
gas
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">krypton</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ >'<span class="explanation-format__original">xenon</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ ></span>
(Other definitions for gas that I've seen before include "Hydrogen, for example" , "Oxygen maybe" , "Nitrogen, say" , "rabbit" , "Something exciting" .)