Etymology
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side-effect (n.)

"subsidiary consequence of an action, etc.," 1884, from side (adj.) + effect (n.). The specific medical use, with reference to drugs, is recorded by 1939.

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effect (n.)
Origin and meaning of effect

mid-14c., "execution or completion (of an act)," from Old French efet (13c., Modern French effet) "result, execution, completion, ending," from Latin effectus "accomplishment, performance," from past participle stem of efficere "work out, accomplish," from assimilated form of ex "out" (see ex-) + combining form of facere "to make, to do" (from PIE root *dhe- "to set, put"). From French, borrowed into Dutch, German, Scandinavian.

From late 14c. as "power or capacity to produce an intended result; efficacy, effectiveness," and in astrology, "operation or action (of a heavenly body) on human affairs; influence." Also "that which follows from something else; a consequence, a result." From early 15c. as "intended result, purpose, object, intent." Also formerly with a sense of "reality, fact," hence in effect (late 14c.), originally "in fact, actually, really." Meaning "impression produced on the beholder" is from 1736. Sense in stage effect, sound effect, etc. first recorded 1881.

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effect (v.)
Origin and meaning of effect

"to produce as a result; to bring to a desired end," 1580s, from Latin effectus, past participle of efficere "work out, accomplish" (see effect (n.)). Related: Effecting; effection; effectible.

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side (v.)

late 15c., "to cut (meat) into sides," from side (n.). The meaning "place oneself on the same side in action or opinion" (usually side with) is attested by c. 1600, from side (n.) in the figurative sense; earlier hold sides (late 15c.); to take sides is from c. 1700. Related: Sided; siding.

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side (n.)

Old English side "flanks of a person, the long part or aspect of anything," from Proto-Germanic *sīdō (source also of Old Saxon sida, Old Norse siða, "flank; side (of meat); coast," Danish side, Swedish sida, Middle Dutch side, Dutch zidje, Old High German sita, German Seite), from adjective *sithas "long" (source of Old English sid "long, broad, spacious," Old Norse siðr "long, hanging down"), from PIE root *se- "long; late" (see soiree).

The "long part of anything" sense is preserved hillside, it also was in 16c.-17c. side-coat "long coat." From 14c. as "lateral half of the body of a slaughtered animal." In reference to bacon, it indicates position relative to the ribs. The meaning "a region, district" is from c. 1400, as in South Side, countryside.

The figurative sense of "position or attitude of a person or set of persons in relation to another" (as in choose sides, side of the story) is recorded by mid-13c. As "an aspect" of anything immaterial (the bright side, etc.), by mid-15c.

The meaning "one of the parties in a transaction" is from late 14c.. The sense of "one of the parties in a sporting contest or game" is from 1690s. The meaning "music on one side of a phonograph record" is attested by 1936. As short for side-dish, by 1848.

The phrase side by side "close together and abreast, placed with sides near together" is recorded from c. 1200. Colloquial on the side "in addition," especially "unacknowledged," with connotations of "illicit, shady," is by 1893.

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side (adj.)

late Old English, "long, broad, spacious; extending lengthwise," from side (n.). Compare Old Norse siðr "long, hanging down." From late 14c. as "being from or toward the side," hence also "subordinate." Also "apart from the main course" of anything, as in side-road (1854); side-trip (1911). In side-eye (by 1922) the notion is "directed sideways."

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side-step (n.)

also sidestep, 1757, "a stepping to the side" (originally in military drill), from side (adj.) + step (n.). The verb is recorded from 1895, "step to one side;" the figurative sense of "evade (an issue), prevaricate" is attested from 1900.

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side-dish (n.)

"dish accessory to the principal one in a course," 1725, from side (adj.) + dish (n.). The restaurant phrase on the side "apart from the main dish" is attested from 1884, in American English.

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side-saddle (n.)

"saddle made for the occupant to ride on with both feet on the same side of the horse," used chiefly by women, late 15c., from side (adj.) + saddle (n.). As an adverb, in ride side-saddle, by 1885.

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side-door (n.)

"door on the side of a building, room, etc.," 1530s, from side (n.) + door.

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