The offer I had by letter (3)
I believe the answer is:
bid
'the offer' is the definition.
(bid is a kind of offer)
'i had by letter' is the wordplay.
'i had' becomes 'i'd' (I'd).
'by' says to put letters next to each other.
'letter' becomes 'b' ().
'id' after 'b' is 'BID'.
(Other definitions for bid that I've seen before include "Make an offer at auction" , "Propose a payment" , "Take part in auction" , "Offer; command" , "Order - offer" .)