Funny turn after onset of dizziness (5)
I believe the answer is:
droll
'funny' is the definition.
(thesaurus)
'turn after onset of dizziness' is the wordplay.
'turn' becomes 'roll' (roll is a kind of turn).
'after' is a charade indicator (letters next to each other).
'onset of' suggests taking the first letters.
The first letter of 'dizziness' is 'd'.
'roll' put after 'd' is 'DROLL'.
(Other definitions for droll that I've seen before include "Clownish" , "Drily witty" , "Funny" , "Mildly amusing" , "Amusing in offbeat way" .)