Jamieson, Fausset and Brown on Titus 3:10

10. heretic--Greek "heresy," originally meant a division resulting from individual self-will; the individual doing and teaching what he chose, independent of the teaching and practice of the Church. In course of time it came to mean definitely "heresy" in the modern sense; and in the later Epistles it has almost assumed this meaning. The heretics of Crete, when Titus was there, were in doctrine followers of their own self-willed "questions" reprobated in Tit 3:9, and immoral in practice.

reject--decline, avoid; not formal excommunication, but, "have nothing more to do with him," either in admonition or intercourse.