Pass comment on former currency unit (7)
I believe the answer is:
expound
'pass comment' is the definition.
'expound' can be an answer for 'comment' (thesaurus). I am not sure about the 'pass' bit.
'former currency unit' is the wordplay.
I cannot really see how this works, but
'former' could be 'ex' (prefix meaning former or onetime) and 'ex' is found within the answer.
'currency' could be 'pound' (as in pound sterling, British currency) and 'pound' is located in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
'on' is the link.
Can you help me to learn more?
(Other definitions for expound that I've seen before include "Elaborate" , "Spell out" , "Put forward detailed argument" , "Set forth, explain in detail" , "Upend ox (anag)" .)