Extended sense of "nonhistorical or mythical story," with or without saints, wonders, and miracles is first recorded late 14c. Meaning "writing or inscription" (especially on a coin or medal) is from 1610s; on a map, illustration, etc., from 1903. To be a legend in (one's) own time is from 1958.
Proto-Indo-European root meaning "to collect, gather," with derivatives meaning "to speak" on the notion of "to gather words, to pick out words."
It forms all or part of: alexia; analects; analogous; analogue; analogy; anthology; apologetic; apologue; apology; catalogue; coil; colleague; collect; college; collegial; Decalogue; delegate; dialect; dialogue; diligence; doxology; dyslexia; eclectic; eclogue; elect; election; epilogue; hapax legomenon; homologous; horology; ideologue; idiolect; intelligence; lectern; lectio difficilior; lection; lector; lecture; leech (n.2) "physician;" legacy; legal; legate; legend; legible; legion; legislator; legitimate; lesson; lexicon; ligneous; ligni-; logarithm; logic; logistic; logo-; logogriph; logopoeia; Logos; -logue; -logy; loyal; monologue; neglect; neologism; philology; privilege; prolegomenon; prologue; relegate; sacrilege; select; syllogism; tautology; trilogy.
It is the hypothetical source of/evidence for its existence is provided by: Greek legein "to say, tell, speak, declare; to count," originally, in Homer, "to pick out, select, collect, enumerate;" lexis "speech, diction;" logos "word, speech, thought, account;" Latin legere "to gather, choose, pluck; read," lignum "wood, firewood," literally "that which is gathered," legare "to depute, commission, charge," lex "law" (perhaps "collection of rules"); Albanian mb-ledh "to collect, harvest;" Gothic lisan "to collect, harvest," Lithuanian lesti "to pick, eat picking;" Hittite less-zi "to pick, gather."
early 15c., "exposition of myths, the investigation and interpretation of myths," from Late Latin mythologia, from Greek mythologia "legendary lore, a telling of mythic legends; a legend, story, tale," from mythos "myth" (a word of unknown origin; see myth) + -logia (see -logy "study"). Meaning "a body or system of myths" is recorded by 1781.
Roman surname of the Junian gens. Its association with betrayal traces to Marcus Junius Brutus (c. 85 B.C.E.-42 B.C.E.), Roman statesman and general and conspirator against Caesar. The Brutus (Englished as Brute) who was the mythological eponymous founder of Britain in medieval legend was said to be a descendant of Aeneas the Trojan.