The first male worker in firm (7)
I believe the answer is:
adamant
'firm' is the definition.
(thesaurus)
'the first male worker' is the wordplay.
'the first male' becomes 'adam'.
'worker' becomes 'ant' (worker is a type of ant).
'adam'+'ant'='ADAMANT'
'in' is the link.
(Other definitions for adamant that I've seen before include "Refusing to change opinion" , "Positive and unrelenting" , "Imaginary rock" , "Legendary rock" , "Stubbornly firm" .)