What's the difference between pillowcase and pillowslip?

Pillowcase

Definition:

(n.) A removable case or covering for a pillow, usually of white linen or cotton cloth.

Example Sentences:

(1) Soon my pillowcases bore rusty coins of nasal drippage.
(2) Photograph: Linkedin Levine said that the cleaners would remove any traces of body fluids inside, along with possessions that might have been contaminated, such as bedsheets, pillowcases, toothbrushes and towels.
(3) "It sounded like a firecracker in a pillowcase," said Peter Smith, a traveller from the Netherlands.
(4) There will be no half-full glasses; no stalagmites of loose change; no convention of shoes in a huddle under the bed, on which the duvet cover will rest as smooth as an airbrushed forehead; and the sheets will always match the pillowcases.
(5) Officers found what they believed to be about 1,102lb of qat, with a street value of at least £15,000, in pillowcases in the boot and back seat of his black Volkswagen.
(6) The pillowcases were taken away for analysis, police said.
(7) Sure, emotion is good, especially since Simon Cowell did something to his face that makes him resemble a haunted pillowcase.
(8) Recovery of radioactivity from the skin surface and from scalp and pillowcase washes was in the range of 41% to 45% of applied dose.
(9) The Citadel military college in South Carolina has said it is suspending eight cadets after photographs were posted on social media showing them wearing pointed white pillowcases resembling the hoods of the Ku Klux Klan .