Etymology
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convention (n.)

early 15c., convencioun, "a formal agreement, covenant, treaty," also "a formal meeting or convention" (of rulers, etc.), also "a private or secret agreement," from Old French convencion "agreement" and directly from Latin conventionem (nominative conventio) "a meeting, assembly; an agreement," noun of action from past-participle stem of convenire "unite, be suitable, agree, assemble," from assimilated form of com "with, together" (see con-) + venire "to come" (from PIE root *gwa- "to go, come").

Originally of princes, powers, and potentates. In diplomacy, of agreements between states, from mid-15c.; of agreements between opposing military commanders from 1780. Meaning "a formal or recognized assembly of persons for a common objective," especially involving legislation or deliberation, is from mid-16c. Conventions were important in U.S. history and the word is attested in colonial writings from 1720s; in reference to political party nomination meetings by 1817 (originally at the state level; national conventions began to be held in the 1830s).

In the social sense, "general agreement on customs, etc., as embodied in accepted standards or usages," it is attested by 1747 (in a bad sense, implying artificial behavior and repression of natural conduct, by 1847). Hence "rule or practice based on general conduct" (1790).

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*gwa- 

*gwā-, also *gwem-, Proto-Indo-European root meaning "to go, come."

It forms all or part of: acrobat; adiabatic; advent; adventitious; adventure; amphisbaena; anabasis; avenue; base (n.) "bottom of anything;" basis; become; circumvent; come; contravene; convene; convenient; convent; conventicle; convention; coven; covenant; diabetes; ecbatic; event; eventual; hyperbaton; hypnobate; intervene; intervenient; intervention; invent; invention; inventory; juggernaut; katabatic; misadventure; parvenu; prevenient; prevent; provenance; provenience; revenant; revenue; souvenir; subvention; supervene; venire; venue; welcome.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit gamati "he goes," Avestan jamaiti "goes," Tocharian kakmu "come," Lithuanian gemu, gimti "to be born," Greek bainein "to go, walk, step," Latin venire "to come," Old English cuman "come, approach," German kommen, Gothic qiman.

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conventionalism (n.)

"mere adherence to convention," 1833, from conventional + -ism.

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de rigueur 

1849, French, literally "of strictness," thus "according to obligation of convention." See rigor.

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are (n.)

metric unit of square measure, 10 meters on each side (100 square meters), 1819, from French, formed 1795 by decree of the French National Convention, from Latin area "vacant piece of ground" (see area).

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convenance (n.)

late 15c., "a covenant or agreement," from French convenance "convention, agreement, convenience," from convenant, present participle of convenir "to come together; join, fit, suit" (see convene). Meaning "conventional propriety" is from 1847.

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conventional (adj.)

late 15c., "of the nature of an agreement," from Late Latin conventionalis "pertaining to convention or agreement," from Latin conventionem (nominative conventio) "a meeting, assembly; agreement," noun of action from past-participle stem of convenire "unite, be suitable, agree, assemble," from assimilated form of com "with, together" (see con-) + venire "to come" (from PIE root *gwa- "to go, come").

Meaning "of the nature of a formal meeting of delegates" is from 1812, now rare; that of "established by social convention, arising out of custom or usage" is from 1761; sense of "following tradition" is from 1831. Of weapons, "non-nuclear," from 1955. Related: Conventionally.

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hectare (n.)

1817, from French hectare "a hundred ares," formed from Latinized form of Greek hekaton "a hundred" (see hecatomb) + Latin area "vacant piece of ground" (see area). A superficial measure equal to 100 ares, coined by decree of the French National Convention in 1795.

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legionnaire (n.)

1818, from French légionnaire, from légion (see legion). Legionnaires' Disease, caused by Legionella pneumophilia, was named after the lethal outbreak of July 1976 at the American Legion convention in Philadelphia's Bellevue Stratford Hotel. Hence also Legionella as the name of the bacterium.

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imprescriptible (adj.)

"inalienable, not subject to law or convention," 1560s, from French imprescriptible (16c.) or a native formation from assimilated form of in- (1) "not, opposite of" + Latin praescriptus, past participle of praescribere "to write beforehand, determine in advance, ordain, dictate" (see prescribe). Usually with right (n.). Related: Imperscriptibility. Alternative imprescribable is attested from 1887.

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