Hostile frenzied action gains time (12)
I believe the answer is:
antagonistic
'hostile' is the definition.
(similar in meaning)
'frenzied action gains time' is the wordplay.
'frenzied' is an anagram indicator.
'time' becomes 't' (abbreviation).
'action'+'gains'+'t'='actiongainst'
'actiongainst' anagrammed gives 'ANTAGONISTIC'.
(Other definitions for antagonistic that I've seen before include "Actively opposing - stag in action (anag)" , "Ill-disposed" , "Actively hostile" .)