One who has dispiriting experience, wasting day (5)
I believe the answer is:
owner
'one who has' is the definition.
(a person who has things)
'dispiriting experience wasting day' is the wordplay.
'dispiriting experience' becomes 'downer' (a depressing situation or person).
'wasting' suggests deleting specific letters.
'day' becomes 'd' (abbreviation for day).
'downer' with 'd' removed is 'OWNER'.
(Other definitions for owner that I've seen before include "One who has something" , "Person with legal title to something" , "Holder, proprietor" , "landlord" , "The one in lawful possession" .)