Witness, seriously cut, bearing pained expression (7)
I believe the answer is:
voucher
'witness' is the definition.
(thesaurus)
'seriously cut bearing pained expression' is the wordplay.
'seriously cut' becomes 'ver' (I can't explain this - if you can you should believe this answer much more).
'bearing' indicates putting letters inside.
'pained expression' becomes 'ouch' (I've seen this in another clue).
'ver' placed around 'ouch' is 'VOUCHER'.
Can you help me to learn more?
(Other definitions for voucher that I've seen before include "Coupon; receipt" , "Ticket" , "Coupon that can be redeemed" , "Something that can be exchanged for goods or services" , "Paper token" .)