IPA: /ˈmoʊstli/
KK: /ˈmoʊstli/
In a way that indicates the largest part or majority of something; generally or usually.
I mostly enjoy reading fiction books in my free time.
Mostly → It is formed from "most" (from Old English *mæst*, meaning greatest in amount or degree) and "-ly" (meaning in the manner of). The word "mostly" means in the manner of being the greatest part or majority.
Think of 'most' as referring to the greatest amount, and '-ly' indicating a manner. So, mostly means in the manner of being the greatest part.