A counselor is someone who gives counsel -- advice, words of wisdom, and so on. Again, counselor contains counsel.
|The Councillors of the Jedi High Council|
When Yoda sat on the the Jedi High Council, he was a councillor. After the dissolution of the Jedi Order, he moved to Dagobah and, later, became Luke's counselor.
* At least, I hope no one ever thought that a woman on the council should be called a councilless or councilatrix.