Strap (5)
'strap' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for thong that I've seen before include "scanty garment" , "Frequently (archaic)" , "article of clothing" , "Narrow strip of leather (or other material)" , "G-string" .)
(Other definitions for truss that I've seen before include "Bind like a chicken" , "Surgical appliance" , "Structure supporting a roof" , "Wing beam of a plane" , "Hay bundle; tomato cluster" .)