Slash cover to access petty cash (7)
I believe the answer is:
solidus
'slash' is the definition.
(synonyms)
'cover to access petty cash' is the wordplay.
I cannot quite see how this works, but
'cover' could be 'lid' (lid is a kind of cover) and 'lid' is found in the answer.
The remaining letters 'sous' 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 solidus that I've seen before include "old coin" , "Oblique stroke, slash" , "Slash symbol" .)