adj. 25B6; adjective
a serious expression : SOLEMN, earnest, grave, sombre, sober, unsmiling, poker-faced, stern, grim, dour, humourless, stony-faced; thoughtful, preoccupied, pensive.
serious decisions : IMPORTANT, significant, consequential, momentous, weighty, far-reaching, major, grave; urgent, pressing, crucial, critical, vital, life-and-death, high-priority.
give serious consideration to this : CAREFUL, detailed, in-depth, deep, profound, meaningful.
a serious play : INTELLECTUAL, highbrow, heavyweight, deep, profound, literary, learned, scholarly; informal heavy.
serious injuries : SEVERE, grave, bad, critical, acute, terrible, dire, dangerous, perilous, parlous; formal grievous.
we're serious about equality : IN EARNEST, earnest, sincere, wholehearted, genuine; committed, resolute, determined.
light-hearted, trivial, superficial, lowbrow, minor, half-hearted.