Offer key identification (3)
I believe the answer is:
bid
'offer' is the definition.
('bid' can be a synonym of 'offer')
'key identification' is the wordplay.
'key' becomes 'b' (eg B major, musical key**).
'identification' becomes 'id'.
'b'+'id'='BID'
(Other definitions for bid that I've seen before include "Make an offer at auction" , "Attempt, offer" , "Sum offered at an auction" , "Take part in auction" , "Tender (for work)" .)