Prison term or grammatical unit (8)
I believe the answer is:
sentence
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">prison term</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >'<span class="explanation-format__original">grammatical unit</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ ></span>
(Other definitions for sentence that I've seen before include "Part of a message" , "Words - said by judge" , "That which ends with a full stop" , "in so many words" , "Court decision on a grammatical structure" .)