Sixties fad seen in old piece (2,3)
I believe the answer is:
op art
'sixties fad' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
'old piece' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'piece' becomes 'part' (synonyms).
'o'+'part'='OP-ART'
'seen in' is the link.
Can you help me to learn more?
(Other definitions for op art that I've seen before include "Nineteen sixties illusory painting style" , "modern paintings" , "Style of abstract painting using illusion etc" , "Illusory works" , "Illusory form of painting" .)