cynic comes from a Greek word meaning “dog-like, currish, churlish.”
The word cynosure comes from a Greek word meaning “dog’s tail.” This was the name given by the Greeks to the northern constellation Ursa Minor, the “Small Bear” in whose tail is the Pole-star, also known as the North Star. Because the North Star is bright and a means of finding the direction of north, the word cynosure acquired the figurative meaning of “something that is bright and serves as a guide.”
In modern usage, a cynic is a person disposed to find fault with everything and to rant about it to everyone. A cynic trusts no one’s sincerity or good intentions. The adjective is cynical; the noun is cynicism.
Unlike cynic, the word cynosure has positive connotations. A cynosure is someone or something that serves for guidance or direction, a “guiding star.