Not many bothered? It's just the opposite (7)
I believe the answer is:
antonym
'just the opposite' is the definition.
(a word's antonym is its opposite)
'not many bothered?' is the wordplay.
'bothered?' is an anagram indicator.
'not'+'many'='notmany'
'notmany' anagrammed gives 'ANTONYM'.
'it's' acts as a link.
(Other definitions for antonym that I've seen before include "A word opposite in meaning to another" , "Nick's could be free" , "For villain, hero is one" , "A word's opposite" , "One's import is contrary" .)