IPA: /ˈwiːdər/
KK: /ˈwiːdər/
A person or tool that removes unwanted plants, known as weeds, from a garden or other area.
The gardener used a weeder to clear the flower beds of pesky weeds.
Weeder → The word is formed from "weed" (from Old English *wēod*, meaning a plant or herb, often one that is undesirable) and "-er" (meaning a person who). A weeder is a person who removes unwanted plants from a garden or field.
Think of someone who removes 'weeds' — that's what a 'weeder' does, as the '-er' indicates a person involved in the action.