Brave young lady left social worker (7)
I believe the answer is:
gallant
'brave' is the definition.
(similar in meaning)
'young lady left social worker' is the wordplay.
'young lady' becomes 'gal' (synonyms).
'left' becomes 'l' (common abbreviation).
'social worker' becomes 'ant' (ants are social insects).
'gal'+'l'+'ant'='GALLANT'
(Other definitions for gallant that I've seen before include "Courageous - politely attentive to women" , "Dashing gentleman" , "Heroic; chivalrous" , "Valiant; courteous" , "Amorous" .)