Other forms: pillowcases
A pillowcase is the washable cover that slips over a pillow. Change the pillowcase, a cotton pillowcase, a spare pillowcase.
It exists so that the pillow itself never has to be washed, which is the whole idea, and it is the item of bedding that should be changed most often because it is against your face. Housewife and Oxford are the two standard British styles.
1nounpillowcaseThe washable cover that slips over a pillow.
“She put clean pillowcases on the pillows before the guests arrived.”
pillowcase is a cover.
Pillow plus case. Pillow is Old English pyle, from Latin pulvinus, a cushion.
From pillow + case.
Etymology from Wiktionary, CC BY-SA