Strapping Republican in den (6)
I believe the answer is:
sturdy
'strapping' is the definition.
(thesaurus)
'republican in den' is the wordplay.
'republican' becomes 'r' (abbreviation).
'in' is an insertion indicator.
'den' becomes 'study' (I've seen this before).
'r' going within 'study' is 'STURDY'.
(Other definitions for sturdy that I've seen before include "Strongly and solidly built" , "Powerful" , "Uncompromising" , "Robust, strong" , "Stalwart, stout, tough" .)