Outline of waist, flipping round figure (3)
I believe the answer is:
two
'figure' is the definition.
(I've seen this before)
'outline of waist flipping round' is the wordplay.
'outline of' means to remove the middle letters (outline refers to the letters on the edges).
'flipping' says the letters should be written in reverse.
'round' becomes 'o' (round can mean a round object).
'waist' with its centre taken out is 'wt'.
'wt' in reverse letter order is 'tw'.
'tw'+'o'='TWO'
(Other definitions for two that I've seen before include "Even number" , "A low number" , "not very many" , "Minimal number of partners" , "A pair (3)" .)