c. 1300, dyscrecyounne, "ability to perceive and understand;" mid-14c., "moral discernment, ability to distinguish right from wrong;" c. 1400, "prudence, sagacity regarding one's conduct," from Old French discrecion and directly from Medieval 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 (earlier in (one's) discretion, late 14c.), from sense of "power to decide or judge, power of acting according to one's own judgment" (late 14c.). The age of discretion (late 14c.) in English law was 14.
adjective and noun word-forming element, in most cases from Latin -arius, -aria, -arium "connected with, pertaining to; the man engaged in," from PIE relational adjective suffix *-yo- "of or belonging to." The neuter of the adjectives in Latin also were often used as nouns (solarium "sundial," vivarium, honorarium, etc.). It appears in words borrowed from Latin in Middle English. In later borrowings from Latin to French, it became -aire and passed into Middle English as -arie, subsequently -ary.
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Definitions of discretionary from WordNet
having or using the ability to act or decide according to your own discretion or judgment;
The commission has discretionary power to award extra funds
(especially of funds) not earmarked; available for use as needed;