List of serious synonyms and serious related words.
abandoned, acute, afire, alarming, ardent, arduous, austere, awe-inspiring, bad, bound, bound and determined, burning, businesslike, cogitative, cognitive, committed, comprehensive, concentrating, concentrative, conceptive, conceptual, conceptualized, consequential, considerable, contemplating, contemplative, critical, crucial, dangerous, dangersome, decided, decisive, decorous, dedicated, deep, definite, deliberating, deliberative, demure, determined, devoted, devout, difficult, dignified, dour, earnest, elevated, excogitating, exhaustive, explosive, faithful, fatal, fateful, fell, fervent, fervid, fiery, flaming, formal, formidable, fraught with danger, frowning, full, genuine, grand, grave, great, grievous, grim, grim-faced, grim-visaged, hearty, heated, heavy, honest, hot, hot-blooded, humorless, ideative, impassioned, important, imposing, in earnest, inspiring, intense, intent, intent on, introspective, irresistible, jeopardous, laborious, life-and-death, life-or-death, lofty, long-faced, loyal, main, majestic, major, maximum, meditating, meditative, menacing, mental, mighty, moderate, momentous, moving, museful, musing, nasty, no joke, no laughing matter, no-nonsense, noble, noetic, obstinate, on fire, operose, parlous, passionate, pensive, perfervid, periculous, perilous, persevering, persistent, plenary, poker-faced, pondering, portentous, powerful, precarious, prehensive, pressing, purposeful, red-hot, reflecting, reflective, relentless, resolute, resolved, ruminant, ruminating, ruminative, sedate, serious-minded, severe, significant, sincere, single-minded, sober, sober-minded, sobersided, solemn, somber, speculative, spirited, staid, stately, steady, stern, stone-faced, straight-faced, straightforward, strenuous, strong, sublime, temperate, tenacious, thinking, thought, thoughtful, threatening, total, tough, ugly, unamusing, unfunny, unsmiling, urgent, vehement, vital, warm, weighty, white-hot, wholehearted, wistful, zealous