Material one found in wonderland, abruptly stifling yell (7)
I believe the answer is:
acrylic
'material one found in' is the definition.
The answer and definition can be both substances as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
'wonderland abruptly stifling yell' is the wordplay.
'wonderland abruptly' becomes 'alic' (I can't justify this - if you can you should believe this answer much more).
'stifling' indicates putting letters inside (some letters get stifled or contained).
'yell' becomes 'cry' (synonyms).
'alic' placed around 'cry' is 'ACRYLIC'.
Can you help me to learn more?
(Other definitions for acrylic that I've seen before include "Shiny paint" , "The synthetic fibre is icy, Carl" , "Pungent acid" , "Textile fibre - icy Carl (anag)" , "Type of paint or textile fibre" .)