Be of use to (5)
I believe the answer is:
avail
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">be of use to</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 avail that I've seen before include "Use to one's advantage" , "(Of no) use or benefit" , "Be of help or advantage" , "Medal (informal)" , "Be of service to" .)