IPA: //ˈkaʊnsələr//
KK: /ˈkaʊnsələr/
A person who is a member of a council, helping to make decisions and govern a community or organization.
The councillor proposed a new plan to improve the local park.
Councillor is formed from "council" (from Old French *conseil*, meaning a group of advisors) and "-or" (meaning a person who). A councillor is a person who is part of a council, typically involved in decision-making or advisory roles.
Think of a 'council' as a group of advisors, and remember that a 'councillor' is simply a person who is part of that group.
No commonly confused words.