fast asleep
adjEtymology
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.
Definitions
Synonym of sound asleep.
The neighborhood
Vish — recursive loop
No curated loop yet for fast asleep. Loops are being traced one word at a time while the ingestion pipeline matures.
sense glosses and etymology drawn from English Wiktionary · source · CC-BY-SA