routine n.

c. 1200, "a way, a road, space for passage," from Old French rute "road, way, path" (12c.), from Latin rupta (via) "(a road) opened by force," broken or cut through a forest, etc., from rupta, fem. past participle of rumpere "to break" (see rupture (n.)).

The sense of "fixed or regular course for carrying things" (originally and for long especially postal, as in mail route) is from 1792, an extension of the meaning "customary path of animals" (early 15c.) itself later extended to sales, collections, delivery of milk or newspapers, etc. OED says the pronunciation that rhymes with "stout" appeared early 19c.

also -in, adjectival word-forming element, Middle English, from Old French -in/-ine, or directly from Latin suffix -inus/-ina/-inum "of, like," forming adjectives and derived nouns, as in divinus, feminus, caninus; from PIE adjectival suffix *-no- (see -en (2)).

The Latin suffix is cognate with Greek -inos/-ine/-inon, and in some modern scientific words the element is from Greek. Added to names, it meant "of or pertaining to, of the nature of" (Florentinus), and so it also was commonly used in forming Roman proper names, originally appellatives (Augustinus, Constantinus, Justinus, etc.) and its descendants in Romanic languages continued active in name-forming. The Latin fem. form, -ina, was used in forming abstracts (doctrina, medicina). Relics of the attempt to continue a distinction between Latin -ina and -inus account for the English hesitation in spelling between -in and -ine.

"a being or becoming routine; action of imposing a routine upon," 1916, noun of action from routinize "subject to a routine, make into a routine" (1893), from routine + -ize.