IPA: /ˈɡeɪn.fəli/
KK: /ˈɡeɪn.fəl.i/
In a way that produces a profit or benefit; profitably.
She found a gainfully employed position that allowed her to support her family.
Gainfully → It is formed from "gain" (from Old French *gaigner*, meaning to earn or acquire) and "-ful" (meaning full of). The word "gainfully" means in a manner that is full of gain or profit, typically referring to employment or work that provides a benefit.
Think of 'gaining' something valuable and remember that 'gainfully' means doing something in a way that is full of gain or profit.