IPA: /ˈɡriːvəsli/
KK: /ˈgrivəsli/
In a way that causes great sadness or suffering; seriously or severely.
The decision to close the school affected the community grievously.
Grievously → It is formed from "grievous" (from Old French *grievous*, meaning serious or severe) and the suffix "-ly" (meaning in a manner of). The word "grievously" means in a serious or severe manner, often referring to something that causes great sorrow or distress.
Think of something being done in a 'serious' way ('grievous') — the '-ly' just means in that manner. This helps you remember that 'grievously' refers to something done in a serious or severe way.