Buy with a favourite sweetheart? (4)

I believe the answer is:
pete
'buy' is the definition.
Both the answer and definition are singular nouns.
Perhaps there's a link between them I don't understand?
'with a favourite sweetheart?' is the wordplay.
'with' means one lot of letters go next to another.
'a favourite' becomes 'pet' ('pet' can be a synonym of 'favourite').
'sweetheart?' becomes 'e' (the heart/centre of 'sweet').
'pet' put next to 'e' is 'PETE'.
Can you help me to learn more?
(Other definitions for pete that I've seen before include "- Sampras, tennis star" , "For his sake" , "-- Sampras, tennis ace" , "- Seeger, US folk singer" , "filmed with his 1 across [DRAGON]" .)
