[uncountable, countable, usually plural] (literary) sleep; a time when somebody is asleep She fell into a deep and peaceful slumber. The phone suddenly roused her from slumber. I don’t want to wake him from his slumbers. We could hear the breathing of someone in a deep slumber. Word Origin Middle English: alteration of Scots and northern English sloom, in the same sense. The -b- was added for ease of pronunciation.