I. noun
Synonyms: earnestness , intentness, serious-mindedness, seriousness
Related Word: attention, interest; enthusiasm, warmth, zeal
Antonyms: jest, play
II. adjective
Synonyms: serious 1, grave, no-nonsense, sedate, sober, sobersided, solemn, somber, staid, weighty
Related Word: ardent, enthusiastic, passionate, pressing, warm, zealous; assiduous, busy, diligent, industrious, perseverant, sedulous; sincere, wholehearted, whole-souled
Contrasted words: buoyant, effervescent, elastic, flippant, light
Antonyms: frivolous
III. noun
Synonyms: pledge 1, pawn, security, token, warrant