Singlet (4)
I believe the answer is:
vest
'singlet' is the definition.
(synonyms)
This is all the clue.
(Other definitions for vest that I've seen before include "Undergarment to put in right of possession" , "Thesaurus compiler" , "Undergarment for upper body" , "Waistcoat (in USA)" , "Upper undergarment, singlet" .)