Fascinating spells describing web? (8)
I believe the answer is:
magnetic
'fascinating' is the definition.
(thesaurus)
'spells describing web?' is the wordplay.
'spells' becomes 'magic' (I've seen this before).
'describing' is an insertion indicator (describe can mean to form the outline of).
'web?' becomes 'net' ('net' can be a synonym of 'web').
'magic' placed around 'net' is 'MAGNETIC'.
(Other definitions for magnetic that I've seen before include "Very attractive or alluring" , "Attracting iron or steel" , "Having the property of attracting iron" , "attractive result" , "Having the power to attract" .)