Pet, informally (4)
I believe the answer is:
fave
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">pet informally</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for fave that I've seen before include "Most popular" , "Best-loved" .)