beauty-sleep

Noun

beauty sleep (countable and uncountable, plural beauty sleeps)

1. (idiomatic, uncountable) Originally, sleep taken before midnight, on the belief that early sleep hours conduce to beauty and health; now (chiefly humorous), sleep at any time needed by one to stay beautiful; (countable) an instance of such sleep.
   • A medical man, who may be called up at any moment, must make sure of his ‘beauty-sleep.’1857, Charles Kingsley, “The Cruise of the Waterwitch”, in Two Years Ago, volume II, Cambridge, Cambridgeshire: Macmillan and Co., →OCLC, page 148
2. (humorous, idiomatic, uncountable) Extra sleep; also (generally), any sleep; (countable) an instance of this; an extra nap.
   • But eager as Kate was for her beauty sleep, the light burned late in her room; and long after she had seen Mrs. Murray snugly tucked in for the night, she sat with Ranald's open letter in her hand, reading it till she almost knew it by heart.1901, Ralph Connor, “A Good True Friend”, in The Man from Glengarry: A Tale of the Ottawa, Toronto, Ont.: The Westminster Company, →OCLC, page 428

   Synonyms:

   beauty rest