Seat I must sit in daily (5)
I believe the answer is:
chair
'seat' is the definition.
(I know that seat can be written as chair)
'i must sit in daily' is the wordplay.
'must sit in' means one lot of letters goes inside another.
'daily' becomes 'char' (both can mean a cleaner).
'i' going within 'char' is 'CHAIR'.
(Other definitions for chair that I've seen before include "Windsor, for example" , "Seat for one person" , "A committee's most important seat" , "Something with legs" , "Top seat of committee" .)