IPA: /ˈhɛvɪli/
KK: /ˈhɛvɪli/
To a large extent or with a lot of weight; often used to describe actions done with great intensity or difficulty.
The rain fell heavily, causing the streets to flood.
Heavily → It is formed from "heavy" (from Old English *hefig*, meaning having great weight) and "-ly" (meaning in a manner of). The word "heavily" means in a manner that is characterized by great weight or density.
Think of something that is 'heavy' — the '-ly' just means in that manner. So, heavily describes doing something in a way that feels weighty.