IPA: /əˈreɪndʒər/
KK: /əˈreɪndʒər/
A person who organizes or puts things in a specific order or arrangement.
The arranger created a beautiful version of the song for the orchestra.
Arranger is formed from "arranger" (from Old French, meaning to put in order) and "-er" (meaning a person who). The word refers to a person who puts things in order or organizes them.
Think of someone who 'puts in order' ('arranger') — that's why an arranger is a person who organizes things.