Silly craze recalled fairly heartlessly (5)
I believe the answer is:
daffy
'silly' is the definition.
(I've seen this before)
'craze recalled fairly heartlessly' is the wordplay.
'craze' becomes 'fad' (synonyms).
'recalled' says the letters should be written backwards.
'heartlessly' means to remove the middle letters.
'fairly' with its centre removed is 'fy'.
'fad' in reverse letter order is 'daf'.
'daf'+'fy'='DAFFY'
(Other definitions for daffy that I've seen before include "Silly, mildly eccentric" , "duck on screen" , "Silly, eccentric (colloq.)" , "Crazy" , "Film duck" .)