Yours, Etc.: Origins and Uses of 8 Sign-Offs
c.1300, dyscrecyun, "moral discernment," from Old French discrecion or directly from Late Latin discretionem (nominative discretio) "discernment, power to make distinctions," in classical Latin "separation, distinction," noun of state from past participle stem of discernere "to separate, distinguish" (see discern). Phrase at (one's) discretion attested from 1570s, from sense of "power to decide or judge" (late 14c.); the age of discretion (late 14c.) in English law was 14.