Fire republican in jacket (6)
I believe the answer is:
blazer
'jacket' is the definition.
(blazer is a kind of jacket)
'fire republican' is the wordplay.
'fire' becomes 'blaze' (blaze is a kind of fire).
'republican' becomes 'r' (abbreviation).
'blaze'+'r'='BLAZER'
'in' acts as a link.
(Other definitions for blazer that I've seen before include "Uniform jacket" , "Man's garment" , "coat?" , "First to trail" , "Light single-breasted (school or club) jacket" .)