Strangely silent recruit (6)
I believe the answer is:
enlist
'recruit' is the definition.
(I know that enlist is a more specific form of the action recruit)
'strangely silent' is the wordplay.
'strangely' indicates anagramming the letters.
'silent' is an anagram of 'ENLIST'.
(Other definitions for enlist that I've seen before include "augment army" , "Join up, sign on" , "Register" , "Sign on -- 13 (anag)" , "Join up in silent way" .)