Notes brought in to purchase rabbit (5)
I believe the answer is:
bunny
'rabbit' is the definition.
(bunny rabbit is a kind of rabbit)
'notes brought in to purchase' is the wordplay.
'notes' becomes 'nn' (I've seen this in other clues).
'brought in' means one lot of letters goes inside another.
'to purchase' becomes 'buy' (synonyms).
'nn' put inside 'buy' is 'BUNNY'.
(Other definitions for bunny that I've seen before include "Young rabbit" , "pet!" , "Child's word for rabbit" , "Bugs this" , "Child's term for a burrower" .)