The queen must keep a home deposit (7)
I believe the answer is:
earnest
'deposit' is the definition.
(earnest can mean a paid deposit)
'the queen must keep a home' is the wordplay.
'the queen' becomes 'ER' (Elizabeth Regina).
'must keep' means one lot of letters goes inside another.
'home' becomes 'nest' (a bird's home).
'er' placed around 'a' is 'ear'.
'ear'+'nest'='EARNEST'
(Other definitions for earnest that I've seen before include "art making money?" , "Art deserving" , "Pledge - far from frivolous" , "promise" , "Sincere; enthusiastic" .)