Unrestrained, a politician breaks into bombast (7)
I believe the answer is:
rampant
'unrestrained' is the definition.
(I've seen this before)
'a politician breaks into bombast' is the wordplay.
'politician' becomes 'MP' (Member of Parliament).
'breaks into' indicates putting letters inside (inserted letters break into the word).
'bombast' becomes 'rant' (synonyms).
'a'+'mp'='amp'
'amp' placed into 'rant' is 'RAMPANT'.
(Other definitions for rampant that I've seen before include "Unchecked (and violent?)" , "On the rampage" , "Unrestrained, flourishing excessively" , "Out of control" , "Spreading unchecked" .)