Having broken the limit Brown, taken in, is aggressive (8)
I believe the answer is:
militant
'is aggressive' is the definition.
(similar in meaning)
'having broken the limit brown taken' is the wordplay.
'having broken' indicates an anagram.
'brown' becomes 'tan' (tan is a kind of brown).
'taken' means one lot of letters goes inside another.
'limit' anagrammed gives 'milit'.
'milit' enclosing 'tan' is 'MILITANT'.
'in' is the link.
(Other definitions for militant that I've seen before include "Aggressive, willing to fight" , "Favouring confrontational methods" , "Belligerent" , "Activist" , "Warring" .)