IPA: /ˈlɛv.əl.ər/
KK: /ˈlɛvələr/
A person or thing that makes something level or equal, often used in a social or political context to refer to someone who advocates for equality.
The reformers were seen as levellers, fighting for the rights of the common people.
Leveller → It is formed from "level" (from Old French *level*, meaning flat or even) and "-er" (meaning a person who). A leveller is a person who makes things level or equal.
Think of someone who makes things 'even' or 'flat' — that's what a leveller does.