Remnant of undergarment I get shortened (7)
I believe the answer is:
vestige
'remnant' is the definition.
(thesaurus)
'undergarment i get shortened' is the wordplay.
'undergarment' becomes 'vest' (vest is a kind of undergarment).
'shortened' means to remove the last letter.
'get' with its final letter taken away is 'ge'.
'vest'+'i'+'ge'='VESTIGE'
'of' acts as a link.
(Other definitions for vestige that I've seen before include "A sign" , "Residual trace" , "(Last) trace" , "Give set for a surviving trace" , "Slight amount, trace" .)