Reverse Dictionary: SERIOUS

ADJECTIVES
► DARK very serious;  aggressive → 1980s Black British sl.
► DEEDY serious, solemn → 1895 chiefly Eng. dial.
► DEEP serious, weighty, important → 1596 obs.
► DINKUM serious → 1962 Aust. sl.
► FAIR DINKUM serious, in earnest → 1934 Aust. sl.
► FELL grave, serious; important, momentous; strange, extraordinary → 1825 Sc.
► GRAVAMINOUS serious, of grave import; grievous, burdensome → 1721 Sc., obs.
► IN NETTLE-EARNEST serious, in deadly earnest → 1838 Sc. 
► INTENSE serious; soulful → 1879 colloq.
► JOCOSERIOUS half serious, half jocular; blending jokes and serious matters → M17
► OLD serious, wise, thoughtful → 1896 Eng. dial.
► SAIR serious, considerable, sad, thoroughgoing → 1776 Sc.
► SAIRIE ► SAIRY ► SARRIE serious, solemn → 1808 Sc. obs.
► SAIRIOUS serious → 1871 Sc.
► SERIOUS AS A HEART ATTACK very serious → 2000 African-American sl.
► SOLEMNCHOLY excessively serious or solemn; melancholy → 1855
► SULLEN serious, solemn → 1583 obs.
► UNLAIGHT serious, doleful, woebegone → 1905 Eng. dial. obs. (Bk.)
► VICIOUS serious → 1980s African-American & teen sl.

ADVERBS
► CAPITALLY seriously, fatally → 1606
► DEEPLY with deep seriousness, solemnly → c1300 obs.
► FAIR DINKUM seriously, honestly; really; truthfully → 1894 Aust. sl.
► FOR FAIR seriously, in reality, earnestly → 1853 Eng. dial.
► HEAVY seriously, gravely → 1563 obs.
► MORTALLY seriously, extremely, intensely → 1930 Amer. dial.

NOUNS
► BIG DEAL, A anything serious, important, or noteworthy → 1988 Aust. sl.
► GAME FACE a look or manner characterized by single-minded seriousness, dedication, or determination → 1950 US colloq.
► HEAVY NUMBER a serious or important person or thing → 1971 sl.
► PONDERITY seriousness, profundity; esp. of speech or writing → 1656 obs.
► PONDEROSITY seriousness, profundity; esp. of speech or writing → 1589
► RATTLER something serious or impressive → 1847 sl.
► SADNESS seriousness, gravity → 1904 Eng. dial. (Bk.)
► SKELETON AT THE FEAST, A a reminder of serious or saddening things in the midst of enjoyment; a source of gloom or depression → 1857

NOUNS – PERSON
► HORN-RIMMED FEMME a serious minded woman → 1942 Amer. students’ sl. (Bk.)
► SOBERSIDES a serious or sedate person → 1705

PHRASES
► I KID YOU NOT implies that the speaker is being absolutely serious; expresses sincerity → 1914 sl., orig. US
► WHEN THE BAND BEGINS TO PLAY when matters become serious → 1892

VERBS
► AGGREGE to make more serious, to aggravate → a1382 obs.
► AGGRIEVE to make more serious; to aggravate → a1425 obs.
► MUMP to talk seriously → M19 sl.
► PULL A KITE to look or be serious → 19C sl.