Belts or elastic support (7)
I believe the answer is:
bolster
'support' is the definition.
(synonyms)
'belts or elastic' is the wordplay.
'elastic' indicates anagramming the letters (the anagram stretches or twists into a new form).
'belts'+'or'='beltsor'
'beltsor' anagrammed gives 'BOLSTER'.
(Other definitions for bolster that I've seen before include "support for head after retiring" , "Shore up" , "Support; long pillow" , "Long thick pillow" , "Chisel - long cushion" .)