Tight-fitting undergarment (6)
I believe the answer is:
corset
'tight-fitting undergarment' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for corset that I've seen before include "Shaping undergarment" , "Tight-fitting ladies' garment" , "female garment!" , "fat controller?" , "Item of underwear" .)