Slipped Sidney the money to hold (4)
I believe the answer is:
slid
'slipped' is the definition.
('slide' can be a synonym of 'slip')
'sidney the money to hold' is the wordplay.
I cannot quite understand how this works, but
'money' could be 'l' (L can mean 'pounds') and 'l' is found within the answer.
The remaining letters 'sid' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for slid that I've seen before include "Skidded, slewed" , "Slipped" , "Moved smoothly along a surface" , "Moved (eg, on ice)" .)