Similar Words to Grievous:

Atrocious
Dangerous
Flagitious
Grave
Heartbreaking
Heartrending
Heavy
Life-threatening
Monstrous
Serious
Severe
Weighty

Definitions of Grievous:

1. Causing fear or anxiety by threatening great harm
2. Causing or marked by grief or anguish
3. Of great gravity or crucial import; requiring serious thought
4. Shockingly brutal or cruel