adverb
1.
in a serious manner
at last settled seriously to work
Synonyms: actively, down, earnestly, for real
Related Word: gravely, soberly, solemnly; intently; vigorously, zealously; determinedly, purposefully, resolutely; fervently, passionately
Idioms: all joking aside, in all seriousness, in earnest
Contrasted words: airily, casually, flippantly, lightly, unconcernedly; carelessly, haphazardly
2.
to a serious extent
the cities are seriously over-crowded
Synonyms: gravely, intensely, severely
Related Word: decidedly, quite, very; dangerously; critically, deplorably, regrettably