Explain in detail former currency (7)
I believe the answer is:
expound
'explain in detail' is the definition.
(I've seen this in another clue)
'former currency' is the wordplay.
'former' becomes 'ex' (prefix meaning former or onetime).
'currency' becomes 'pound' (as in pound sterling, British currency).
'ex'+'pound'='EXPOUND'
(Other definitions for expound that I've seen before include "Explain and interpret" , "Upend ox (anag)" , "Elucidate" , "Elaborate" , "Spell out" .)