IPA: /ˈtrɪmər/
KK: /ˈtrɪmɚ/
A tool or device used to cut or trim something, often used for gardening or woodworking.
He used a trimmer to shape the hedges in his garden.
Trimmer → It is formed from "trim" (from Old English *trymman*, meaning to make neat or tidy) and "-er" (meaning a person who). A trimmer is a person who makes something neat or tidy, often by cutting or shaping it.
Think of someone who makes things neat and tidy — that's what a trimmer does, as they are a person who 'trims'.