Mark’s weary in the end and chilling (5)
I believe the answer is:
scary
'chilling' is the definition.
('scary' can be a synonym of 'chilling')
'mark's weary in the end' is the wordplay.
'mark' becomes 'scar' ('scar' can be a synonym of 'mark').
'in the end' indicates one should take the final letters.
The final letter of 'weary' is 'y'.
'scar'+'y'='SCARY'
'and' acts as a link.
(Other definitions for scary that I've seen before include "Fearsome" , "Hair-raising" , "Alarming, maybe paranormal" , "spook" , "[SPICE]" .)