Turned to a small joke (4)
I believe the answer is:
spun
'turned' is the definition.
(I've seen this before)
'a small joke' is the wordplay.
'a small' becomes 's' (abbreviation - e.g. clothes size).
'joke' becomes 'pun' (punning is a kind of joking).
's'+'pun'='SPUN'
'to' is the link.
(Other definitions for spun that I've seen before include "Drawn out and twisted (like yarn)" , "Made up (a yarn)" , "(Of cotton/wool) twisted into threads" , "Twirled" , "did quick turn" .)