Twister undecided over a swindle (7)
I believe the answer is:
tornado
'twister' is the definition.
('tornado' can be a synonym of 'twister')
'undecided over a swindle' is the wordplay.
'undecided' becomes 'torn' (someone deliberating between two options is torn).
'over' says to put letters next to each other.
'swindle' becomes 'do'.
'torn'+'a'+'do'='TORNADO'
(Other definitions for tornado that I've seen before include "squall" , "Dreadful blow" , "Typhoon" , "RAF fighter; whirlwind" , "Hurricane" .)