Not relaxed (5)
I believe the answer is:
tense
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">not relaxed</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I know this)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for tense that I've seen before include "perfect, perhaps" , "not together?" , "Anxious, nervous" , "Nervous or tight" , "Verb form, indicates time" .)