Not long ago referring to coin, extremely low-key (8)
I believe the answer is:
recently
'not long ago' is the definition.
(I've seen this before)
'referring to coin extremely low-key' is the wordplay.
'referring to' becomes 're'.
'coin' becomes 'cent' (cent is a kind of coin).
'extremely low-key' becomes 'ly' (I can't justify this - if you can you should believe this answer much more).
're'+'cent'+'ly'='RECENTLY'
Can you help me to learn more?
(Other definitions for recently that I've seen before include "Not so long since" , "In the near past" , "Adverb meaning not long ago" , "Lately" , "Happening not long ago" .)