Twister split American party (7)
I believe the answer is:
tornado
'twister' is the definition.
(term for a tornado)
'split american party' is the wordplay.
'split' becomes 'torn' (I've seen this in other clues).
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'party' becomes 'do' (do can informally mean a party).
'torn'+'a'+'do'='TORNADO'
(Other definitions for tornado that I've seen before include "lot of wind" , "wind-up" , "A violent and destructive whirlwind" , "Destructive weather" , "Tempest'" .)