Penny in old money chucked back by such a fool (5)
I believe the answer is:
april
'such a fool' is the definition.
(as in April Fools' Day)
'penny in old money chucked back' is the wordplay.
'penny' becomes 'p'.
'in' is an insertion indicator.
'old money' becomes 'lira' (former currency of Italy).
'chucked back' shows that the letters should be reversed in order.
'p' going into 'lira' is 'lirpa'.
'lirpa' backwards is 'APRIL'.
'by' acts as a link.
(Other definitions for april that I've seen before include "time of the year" , "Eliot's 'cruellest month'" , "''All in an ... evening / ... airs were abroad'' (by Katherine Tynan)" , "First month of the year with 30 days" , "Fourth month" .)