Flexible cats lie around (7)
I believe the answer is:
elastic
'flexible' is the definition.
('elastic' can be a synonym of 'flexible')
'cats lie around' is the wordplay.
'around' indicates an anagram.
'cats'+'lie'='catslie'
'catslie' anagrammed gives 'ELASTIC'.
(Other definitions for elastic that I've seen before include "Pliable" , "Material for bands" , "It's lace (anag.)" , "Ductile" , "Kind of band" .)