Insurgent put base of bomb in rock (5)
I believe the answer is:
rebel
'insurgent' is the definition.
(synonyms)
'base of bomb in rock' is the wordplay.
'base of' suggests taking the first letters.
'in' is an insertion indicator.
'rock' becomes 'reel' (I've seen this before).
The initial letter of 'bomb' is 'b'.
'b' inserted into 'reel' is 'REBEL'.
'put' acts as a link.
(Other definitions for rebel that I've seen before include "Insurgent, renegade" , "Disobey" , "revolutionary" , "Refuse orders" , "Unconventional type" .)