Girl's assistance accepted by adult males (6)
I believe the answer is:
maiden
'girl's' is the definition.
'assistance accepted by adult males' is the wordplay.
'assistance' becomes 'aid' (synonyms).
'accepted by' indicates putting letters inside (inserted letters are accepted).
'adult males' becomes 'men' ('man' can be a synonym of 'adult male').
'aid' put within 'men' is 'MAIDEN'.
(Other definitions for maiden that I've seen before include "No-score over" , "Six dot balls" , "Earliest - unmarried" , "Unmated; runless over" , "First, inaugural" .)