Taut or rigid (5)
I believe the answer is:
tense
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">taut</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(similar in meaning)</span><br/ ><br/ >'<span class="explanation-format__original">rigid</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ ></span>
(Other definitions for tense that I've seen before include "Attribute of verbs signalling time" , "Maybe past" , "Verb form; uptight" , "not together?" , "Nerve-racking" .)