IPA: /ˈɡriːvəs/
KK: /ˈgrivəs/
Causing great sadness, pain, or suffering; very serious or severe.
The accident resulted in grievous injuries to several people.
Grievous → It is formed from "grieve" (from Old French *grever*, meaning to burden or oppress) and the suffix "-ous" (meaning full of). The word "grievous" means full of grief or causing great sorrow or pain.
Think of being 'full of grief' — 'grieve' means to feel sorrow, and '-ous' indicates that something is characterized by that feeling.