Synonyms of serious

1 Syllable

set, ter, bound, staid, stern, grim

2 Syllables

pressing, urgent, big-deal, sober, studious, intent, profound, staider, steady, earnest, staidest, grave, hell-bent, stand-out, downbeat, solemn, parlous, heaton, pointful, thoughtful, weighty, doozie, somber, deadpan, honest, heat-on, devout, splasher, subdued, front-page, fervent

3 Syllables

important, notable, frontpage, distingue, high-power, celebrious, nameable, long-faced, funereal, unsmiling, onerous, heart-and-soul, clear-headed, called-for, substantial, genuine, newsworthy, dead-level, soberest, austere, severest, severer, heightened, composed, meaningful, demurer, resolved, jeopardous, terrible, sedate, heart-rending, severe, dangerous, museful, distingué, sincerest, earth-shaking, pensive, hurry-up, life-and-death, profoundest, soberer, earthshaking, sincere, bigtime

4 Syllables

incurable, resolute, earthshattering, pokerfaced, unhumorous, overtaxing, top-priority, determined, remediless, dangersome, reflective, dirgelike, iron-handed, significant, wholehearted, matter-of-fact, all-important, consequential, earth-shattering, memorable, high-priority, no-nonsense, noteworthy, venerable, high-profile, major-league

5 Syllables

businesslike, inoperable, contemplative, ruminative, immedicable, deliberate, applicative, meditative, unsentimental, unimpassioned, unidealistic

6 Syllables

irrecoverable, unrecoverable