Cover with £1 note! (3)
I believe the answer is:
lid
'cover' is the definition.
(I know that cover can be written as lid)
'with ps1 note' is the wordplay.
'with' says to put letters next to each other.
'psl' becomes 'li' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'note' becomes 'D' (musical note).
'li' next to 'd' is 'LID'.
Can you help me to learn more?
(Other definitions for lid that I've seen before include "Top or cover" , "Removable top" , "Removable cover of a container" , "Top for bottle or eye protector" , "Receptacle cover" .)