One whole thing (4)
I believe the answer is:
unit
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">one whole thing</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for unit that I've seen before include "Whole - group" , "Element or part" , "A single self-contained item" , "Any division of quantity accepted as a standard of measurement" , "Single piece - kitchen cabinet" .)