"of or pertaining to the side," early 15c., from Old French latéral (14c.) and directly from Latin lateralis "belonging to the side," from latus (genitive lateris) "the side, flank of humans or animals, lateral surface," a word of uncertain origin. Specific sense "situated on either side of the median vertical longitudinal plane of the body" [Century Dictionary] is from 1722.

As a noun, from 1630s, "a side part;" as a type of pass to the side in U.S. football, it is attested from 1934 (short for lateral pass). Related: Laterally.

also side-car, 1881, "conveyance in which the seats face to the side;" see side (n.) + car (n.). Attested by 1903 as "vehicle designed to be attached to the side of a motorcycle to accommodate another passenger." By 1928 as the name of a cocktail.

"sure to have the desired effect" (often of medicines), 1520s, from Latin efficaci-, stem of efficax "powerful, effectual, efficient," from stem of efficere "work out, accomplish" (see effect (n.)) + -ous. Related: Efficaciously; efficaciousness.

"the placing of clauses one after another without connecting words to indicate their relation," 1838, from Greek parataxis "a placing side by side, a placing in line of battle," from stem of paratassein "to place side by side," from para- "beside" (see para- (1)) + tassein "to arrange" (see tactics). Related: Paratactic.

"the side of the road," c. 1400, from way (n.) + side (n.). To fall by the wayside is from Luke viii.5.

"crosswise, from side to side," late 15c., from a- (1) + thwart (v.). In nautical use, "across the line of a ship's course."

also side-arm, "done with the swing of the arm extended sideways," 1908, from side (adj.) + arm (n.1).

"the side or border of a road," 1744, from road (n.) + side (n.). As an adjective by 1810.

also down side, 1680s, "underside;" see down (adv.) + side (n.). Meaning "drawback, negative aspect" is attested by 1995.

"side of a ship" (technically, "the side of a ship above the water, between the bow and the quarter"), 1590s, from broad (adj.) + side (n.); thus "the artillery on one side of a ship all fired off at once" (1590s, with figurative extensions). Two words until late 18c.

In reference to things other than ships, 1630s. But the oldest-recorded sense in English is "sheet of paper printed on one side only" (1570s). As an adverb by 1870; as an adjective by 1932. As a verb from 1930, "skid sideways" (intransitive); transitive sense "strike broadside, collide with the side of" is by 1970.