Collector opposed mine, right away (9)
I believe the answer is:
antiquary
'collector' is the definition.
(someone who collects antiques)
'opposed mine right away' is the wordplay.
'opposed' becomes 'anti' (similar in meaning).
'mine' becomes 'quarry' (synonyms).
'right' becomes 'r' (common abbreviation).
'away' is a deletion indicator.
'quarry' with 'r' taken out is 'quary'.
'anti'+'quary'='ANTIQUARY'
(Other definitions for antiquary that I've seen before include "seller of the old-fashioned?" , "Dealer in or collector of old things" , "Specialist in old items" , "Expert in (or collector of) old artefacts" .)