"pertaining to Rome or the Roman people," 1708, originally and usually in reference to languages or dialects descended from Latin, from Latin Romanicus, from Romanus "Roman" (see Roman; also compare romance (n.)).
noun and adjective, Old English, "of or pertaining to ancient Rome; an inhabitant or native of ancient Rome," from Latin Romanus "of Rome, Roman," from Roma "Rome" (see Rome). The adjective is c. 1300, from Old French Romain. The Old English adjective was romanisc, which yielded Middle English Romanisshe.
In reference to a type of numeral (usually contrasted to Arabic) it is attested from 1728; as a type of lettering (based on the upright style typical of Roman inscriptions, contrasted to Gothic, or black letter, and italic) it is recorded from 1510s. The Roman nose, having a prominent upper part, is so called by 1620s. The Roman candle as a type of fireworks is recorded from 1834. Roman Catholic is attested from c. 1600, a conciliatory formation from the time of the Spanish Match, replacing Romanist, Romish which by that time had the taint of insult in Protestant England.
c. 1300, romaunce, "a story, written or recited, in verse, telling of the adventures of a knight, hero, etc.," often one designed principally for entertainment, from Old French romanz "verse narrative" (Modern French roman), also "the vulgar language," originally an adverb, "in the vernacular language," from Vulgar Latin *romanice scribere "to write in a Romance language" (one developed from Latin instead of Frankish), from Latin Romanicus "of or in the Roman style," from Romanus "Roman" (see Roman).
The sense evolution is because medieval vernacular tales (as opposed to Latin texts) usually told chivalric adventures full of marvelous incidents and heroic deeds. "The spelling with -aunce, -ance was very early adopted in English, probably on the analogy of abstract sbs." [OED].
In reference to literary works, in Middle English often meaning ones written in French but also applied to native compositions. The literary sense was extended by 1660s to "a love story, the class of literature consisting of love stories and romantic fiction." Meaning "imaginative, adventurous quality" first recorded 1801; that of "love affair" is from 1916. Romance novel is attested by 1820. Compare Romance (adj.).
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Definitions of Romanic from WordNet
of or relating to or derived from Rome (especially ancient Rome);