Mark is entertained by Pontins crib evening (8)
I believe the answer is:
inscribe
'mark' is the definition.
(I know that inscribe is a more specific form of delineate)
'entertained by pontins crib evening' is the wordplay.
'entertained by' indicates the answer is hidden within the clue (the clue hosts or entertains the answer).
'INSCRIBE' can be found hidden inside 'pontins crib evening'.
'is' is the link.
(Other definitions for inscribe that I've seen before include "Write upon, formally perhaps" , "Write or cut words into a surface" , "Engrave; dedicate" , "Write a dedication to someone in (a book)" , "autograph" .)