absorbed in work

Translations
погружённый в работу
He was completely absorbed in work and didn't notice the time passing.
Он был полностью погружён в работу и не заметил, как прошло время.
Definitions
Fully focused and engaged in one's tasks or responsibilities, often to the extent of being unaware of one's surroundings or other activities.
Words
work

noun
работа
absorb

verb
впитывать