Invested with singlet (4)
I believe the answer is:
vest
'singlet' is the definition.
(synonyms)
'invested with' is the wordplay.
'with' says the answer is hidden in the clue.
'VEST' is hidden in the letters of 'invested'.
(Other definitions for vest that I've seen before include "Undergarment for upper body" , "Clothing" , "American version of waistcoat" , "Undershirt, singlet" , "Undergarment to put in right of possession" .)