Rich Irish forged coin (6)
I believe the answer is:
ironic
'rich' is the definition.
(I've seen this before)
'irish forged coin' is the wordplay.
'irish' becomes 'IR' (abbreviation).
'forged' is an anagram indicator.
'coin' with letters rearranged gives 'onic'.
'ir'+'onic'='IRONIC'
(Other definitions for ironic that I've seen before include "Strangely apt or inapt" , "'Wry, incongruous (6)'" , "Strange and perverse" , "turning out unexpectedly" , "Paradoxically amusing" .)