Material wonderful, almost sumptuous (6)
I believe the answer is:
fabric
'material' is the definition.
(I know that material can be written as fabric)
'wonderful almost sumptuous' is the wordplay.
'wonderful' becomes 'fab' (slang abbreviation of fabulous).
'almost' means to remove the last letter (most of the word but not all of it).
'sumptuous' becomes 'rich' (similar in meaning).
'rich' with its last letter taken away is 'ric'.
'fab'+'ric'='FABRIC'
(Other definitions for fabric that I've seen before include "Woven textile" , "Knitted or woven fabric" , "Manufactured cloth" , "Cotton or tweed, say" , "Silk or satin, say" .)