Silent brother (5)
I believe the answer is:
harpo
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">silent brother</span>' is the definition.<br/ ><span class="explanation-format__explanation">(mute Marx brother Harpo Marx)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for harpo that I've seen before include "one from family of comedians" , "The mute Marx Brother" , "One of the Marx Brothers" , "The dumb Marx brother" , "Silent Marx brother" .)