Stretchy cats lie sprawling (7)
I believe the answer is:
elastic
'stretchy' is the definition.
(something elastic can be stretched)
'cats lie sprawling' is the wordplay.
'sprawling' indicates anagramming the letters.
'cats'+'lie'='catslie'
'catslie' anagrammed gives 'ELASTIC'.
(Other definitions for elastic that I've seen before include "Scale it (anag.)" , "Narrow strip of rubber" , "Like one across" , "Flexible rubber strip" , "Pliable" .)