-ary/-ory

Makes adjectives meaning relating to, or nouns for associated people, things, or places.

Spelled -ary, -ory · Latin -arius and -orius, adjective endings meaning connected with; related noun endings named people, things, and places

Latin -arius marked association: an epistolary novel uses letters, an auxiliary gives help, and a tributary supplies tribute or water.

Words built from it

epistolary — Related to letters, especially a story told through letters.
Latin epistola (letter) + -aris (relating to) → epistolaris → epistolary
desultory — Moving between subjects or activities without a steady plan.
Latin desultor (a rider who leaps between horses) + -ius → desultorius → desultory
peremptory — Insisting on obedience or acceptance without discussion.
Latin perimere (put an end to), participle peremptus → peremptorius (decisive) → peremptory
tributary — A stream that feeds a larger river; also, paying tribute.
Latin tributum (tribute) + -arius → tributarius (paying tribute) → tributary
sedentary — Involving much sitting and little physical movement.
Latin sedere (sit) → sedentarius (connected with sitting) → sedentary
arbitrary — Based on personal choice rather than a consistent rule or reason.
Latin arbiter (judge) + -arius → arbitrarius (depending on a judgment) → arbitrary
auxiliary — Providing extra help or support.
Latin auxilium (help) + -arius → auxiliarius → auxiliary

category — From Greek kategoria, originally accusation or predication, through French catégorie; its final letters do not represent Latin -ory.