Passionate, well-built chaps kept in check (8)
I believe the answer is:
vehement
'passionate' is the definition.
(thesaurus)
'well-built chaps kept in check' is the wordplay.
'well-built chaps' becomes 'hemen' (a he-man is a muscular man).
'kept in' is an insertion indicator.
'check' becomes 'vet' (I've seen this before).
'hemen' inserted into 'vet' is 'VEHEMENT'.
(Other definitions for vehement that I've seen before include "Violent" , "Passionate, intense" , "Showing strong feeling, intense in speech" , "Forceful, ardent" , "Ardently forceful" .)