Confess to making regressive quip after expression of pain (5)
I believe the answer is:
ownup
'confess' is the definition.
(I've seen this before)
'regressive quip after expression of pain' is the wordplay.
'regressive' says the letters should be written backwards (to regress is to go backwards).
'quip' becomes 'pun' (I've seen this in other clues).
'after' means one lot of letters go next to another.
'expression of pain' becomes 'ow'.
'pun' back-to-front is 'nup'.
'nup' put after 'ow' is 'OWNUP'.
'to making' is the link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Another definition for ownup that I've seen is " confess".)