councilor (n.)

"a member of a council," early 15c., an alteration of counselor by assimilation to council.

The distinction of form and sense (councilor, one of a council, counselor, one who counsels) is modern; there is no OF. or L. form corresponding to councilor (L. as if *conciliarius) as distinguished from counselor (L. consiliarius). [Century Dictionary]

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