Fascinating stretch cover (12)
I believe the answer is:
spellbinding
'fascinating' is the definition.
('spellbind' can be a synonym of 'fascinate')
'stretch cover' is the wordplay.
'stretch' becomes 'spell' (I've seen this in another clue).
'cover' becomes 'binding' (cover of a book).
'spell'+'binding'='SPELLBINDING'
(Other definitions for spellbinding that I've seen before include "Enthralling" , "Engrossing" , "Fascinating" .)