a member of a council
"The new councillor attended her first meeting to discuss the city's budget."
A member of a council.
"As a new councillor, she attended her first meeting to learn about local zoning laws."
The word councillor is a later alteration of the original spelling counsellor to match its related noun, council. This change was made because speakers mistakenly analyzed it as being formed from "council" plus the suffix "-or.