Reject sandwich needing new filling (4)
I believe the answer is:
snub
'reject' is the definition.
(I know that snub is a type of reject)
'sandwich needing new filling' is the wordplay.
I cannot quite see how this works, but
'new' could be 'n' (common abbreviation eg NT for New Testament) and 'n' is present in the answer.
'sandwich' could be 'sub' (sub is a kind of sandwich) and 'sub' is located in the remaining letters.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for snub that I've seen before include "Rebuff insultingly" , "Cold-shoulder" , "Rude rejection" , "16" , "Insult; blunt (nose)" .)