This is the 3593rd most frequent Russian word.
сном
The Russian word "сном" means "with sleep" or "by sleep" (instrumental case of "сон" - sleep).
сном describes an imagined scenario or illusion often associated with dreams.
Мы были уверены, что это был сон, а не реальность.
We were sure that it was a dream, not reality.
сном is part of the noun 'сон', meaning 'dream'. Here it represents the thing seen while sleeping.
Этой ночью мне приснился странный сон.
Last night I had a strange dream.
сном refers to 'сон', indicating the state or process of sleeping.