One increasing guineas or shillings? (8)
I believe the answer is:
extender
'one increasing guineas or shillings?' is the definition.
The definition suggests a singular noun which matches the answer.
'one' is the wordplay.
I cannot quite understand how this works, but
'one' could be 'er' (I've seen this in other clues) and 'er' is found within the answer.
The remaining letters 'extend' is a valid word which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for extender that I've seen before include "stretcher required?" , "one to reach out" .)