Plural "is" (3)
I believe the answer is:
are
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">plural is</span>' is the definition.<br/ ><span class="explanation-format__explanation">(plural form of the verb 'is')</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for are that I've seen before include "(They/you/we) exist" , "Unit of land measure equal to 100 square metres" , "Is, in the plural" , "Exist; square measure" , "is for more than one" .)