Finish in effort to be with it (6)
I believe the answer is:
trendy
'with it' is the definition.
(thesaurus)
'finish in effort' is the wordplay.
'finish' becomes 'end' ('end' can be a synonym of 'finish').
'in' is an insertion indicator.
'effort' becomes 'try' ('try' can be a synonym of 'effort'**).
'end' going inside 'try' is 'TRENDY'.
'to be' is the link.
(Other definitions for trendy that I've seen before include "With it, a la mode" , "Informally, following the fashions" , "In accordance with the latest fad" , "Consciously fashionable" , "Informally in the latest fashion" .)