One-piece garment (7)
I believe the answer is:
leotard
'one-piece garment' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for leotard that I've seen before include "Gymnastic garment" , "Dance garment" , "Tight-fitting garment, for gymnasts say" , "Acrobat costume" , "Skin-tight garment worn by acrobats" .)