Chance one day to stop stress (8)
I believe the answer is:
accident
'chance' is the definition.
(I've seen this before)
'one day to stop stress' is the wordplay.
'one' becomes 'i' (Roman numeral).
'day' becomes 'd' (abbreviation for day).
'to stop' indicates putting letters inside.
'stress' becomes 'accent' (accent can mean to emphasise or stress).
'i'+'d'='id'
'id' placed into 'accent' is 'ACCIDENT'.
(Other definitions for accident that I've seen before include "Chance misfortune or injury" , "Unforeseen mishap" , "fluke" , "Chance event with no apparent cause" , "Fortune" .)