IPA: /əˈpiːlər/
KK: /əˈpilər/
A person who requests a decision or change, often in a legal or formal context.
The appealer submitted their case to the higher court for review.
Appealer is formed from "appeal" (from Old French *apeler*, meaning to call or summon) and "-er" (meaning a person who). An appealer is a person who calls or summons for something, often in a legal context.
Think of someone who is 'calling' ('apeler') for help or a decision — that's what an appealer does.