Good man's fit and strong (6)
I believe the answer is:
stable
'strong' is the definition.
(thesaurus)
'good man's fit' is the wordplay.
'good man' becomes 'st'.
'fit' becomes 'able' ('able' can be similar in meaning to 'fit').
'st'+'able'='STABLE'
'and' acts as a link.
(Other definitions for stable that I've seen before include "farm building" , "far from bats?" , "Sure!" , "Secure - fast - horses" , "Maintaining equilibrium" .)