Confined to wager, very small note (7)
I believe the answer is:
between
'confined to' is the definition.
(confined within an area or range)
'wager very small note' is the wordplay.
'wager' becomes 'bet' (synonyms).
'very small' becomes 'wee' ('wee' is a Scottish word for small).
'note' becomes 'n' (abbreviation).
'bet'+'wee'+'n'='BETWEEN'
(Other definitions for between that I've seen before include "In the middle (of)" , "Don't tell anyone else..." , "Amid" , "In the period separating (two events)" , "Been wet (anag.)" .)