Belt that often goes missing in laundry (4)
I believe the answer is:
sock
I believe this clue is a double definition.
'belt' is the first definition.
(both can mean to hit)
'that often goes missing in laundry' is the second definition.
(socks are easily lost during the laundry process)
(Other definitions for sock that I've seen before include "Item of footwear" , "One going into Oxford maybe" , "Foot garment" , "Strike, hose" , "Hit; horse's leg marking" .)