Pigeonhole (5)
I believe the answer is:
label
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">pigeonhole</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for label that I've seen before include "Designate" , "Means of identifying" , "Classifying name" , "Put a name to" , "attachment to the Christmas parcel" .)