This is the 3563rd most frequent Russian word.
серьезного
"Serious" (genitive, accusative, or masculine adjective form).
Describes the seriousness of a personality type or disposition.
Он оказался серьезного характера.
He turned out to have a serious character.
Indicates the necessity of a serious manner or effort.
Это требует серьезного подхода.
This requires a serious approach.
Refers to someone's facial expression displaying seriousness.