Ruddy problem in retaining copper penny from former days (8)
I believe the answer is:
rubicund
'ruddy' is the definition.
(synonyms)
'problem in retaining copper penny from former days' is the wordplay.
'problem' becomes 'rub'.
'retaining' indicates putting letters inside.
'copper' becomes 'cu' (chemical symbol).
'penny from former days' becomes 'd' (abbreviation for the pre-decimal penny).
'in' placed around 'cu' is 'icun'.
'rub'+'icun'+'d'='RUBICUND'
(Other definitions for rubicund that I've seen before include "Florid" , "Of complexion, red or ruddy" , "Ruddy, red-faced" .)