Measureless chasm (5)
I believe the answer is:
abyss
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">measureless chasm</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for abyss that I've seen before include "Seemingly bottomless chasm" , "Deep hole, seems bottomless" , "great depth" , "deep depression" , "Measureless chasm" .)