IPA: /ˈweɪstfəli/
KK: /ˈweɪstfəli/
In a way that uses more resources than necessary, often leading to loss or damage.
He spent his money wastefully on things he didn't need.
Wastefully → It is formed from "waste" (from Old English *wæste*, meaning to waste or to be unproductive) and "-fully" (meaning in a manner full of). The word "wastefully" means in a manner that is full of waste or unproductive use of resources.
Think of being 'full of waste' — 'waste' means to use resources unproductively, and '-fully' describes the manner of doing so.