What word does your mother always say?
1560s, "able to manage for oneself, fertile in expedients," from shift (n.1) in secondary sense of "dodge, trick, artifice" + -y (2). Meaning "habitually using dishonest methods, characterized by trickery" first recorded 1837. In a sense "prone to shifting," of the wind, used from 1884. Related: Shiftily; shiftiness.