Meanings
Synonyms & antonyms
adjectiveSynonym of sound asleep.
More synonyms by meaning
adjectivesleeping deeply
Synonym sets from Open English WordNet, CC BY 4.0.
Origin
The original sense of fast in this term is the "firmly gripped or anchored" sense, thus as if stuck fast (embedded firmly) in sleep, but the homonymy with fast as in "quickly" happens to dovetail with the fact that a very tired person will archetypally fall asleep quickly, which tends to color this term with a connotation of falling asleep both quickly and deeply.
Full word history & related roots →Translations
Chinese Mandarin 沉睡, 熟睡
- 沉睡 (chénshuì)in a deep sleep
- 熟睡 (shúshuì)in a deep sleep
Dutch als een blok slapen
- als een blok slapenin a deep sleep
Finnish sikiunessa, sikeässä unessa
- sikiunessain a deep sleep
- sikeässä unessain a deep sleep
German in tiefem Schlaf
- in tiefem Schlafin a deep sleep
Romanian într-un somn adânc
- într-un somn adâncin a deep sleep
Cite this entry
fast asleep. (n.d.). In WatkinsX Dictionary. Retrieved November 4, 2026, from https://dictionary.watkinsx.com/word/fast%20asleep
“fast asleep.” WatkinsX Dictionary, https://dictionary.watkinsx.com/word/fast%20asleep. Accessed November 4, 2026.
WatkinsX Dictionary, s.v. “fast asleep,” accessed November 4, 2026, https://dictionary.watkinsx.com/word/fast%20asleep.
Source: fast asleep on Wiktionary, CC BY-SA 4.0.