serious

adj

1. pensive, deep in thought, thoughtful, wrinkle-browed, reflective, meditative; engrossed, absorbed, preoccupied.

2. grave, somber, grim, unsmiling, unlaughing; sedate, staid, dour, severe, stern; solemn, sober, sober as a judge, straight-faced, poker-faced, long-faced.

3. earnest, resolute, firm, definite, decided; sincere, honest, genuine, real, Inf. for real; intent, intense, fervent, deep, heartfelt.

4. heavy, weighty, difficult, involved, complex, challenging.

5. important, significant, momentous, of moment, consequential, of consequence, not to be laughed at, no laughing matter; crucial, vital, fateful, life-and-death.

6. critical, acute, bad, dangerous, perilous, hazardous, menacing; scary, fearful, alarming; precarious, touchy, ticklish, touch-and-go.