Contemptuous expression of witness withholding name (5)
I believe the answer is:
sneer
'contemptuous expression' is the definition.
(I've seen this before)
'witness withholding name' is the wordplay.
I cannot really understand how this works, but
'name' could be 'n' (common abbreviation e.g. on forms) and 'n' is present in the answer.
'witness' could be 'see' (synonyms) and 'see' is present in the leftover letters.
A single letter 'r' remains which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'of' is the link.
Can you help me to learn more?
(Other definitions for sneer that I've seen before include "Be derisive; Sheridan's Critic" , "Taunt" , "Speak contemptuously" , "Deride, jeer" , "sound scornful" .)