taru-adjective, adverb taking the 'to' particle
fast asleep; sound asleep; dead to the world
Describes a state of deep, oblivious sleep. Often used in literary or descriptive contexts with the particle と.
He was so tired that he slept soundly on and on.
The baby was fast asleep and didn't notice any noise.
Full kanji repetition form; less common than 昏々.
Reduplication of 昏 (こん, 'dark, dim'), emphasizing a state of deep unconsciousness akin to darkness. The exact historical derivation is uncertain.