mid-14c., logike, "branch of philosophy that treats of forms of thinking; the science of distinction of true from false reasoning," from Old French logique (13c.), from Latin (ars) logica "logic," from Greek (he) logike (techne) "(the) reasoning (art)," from fem. of logikos "pertaining to speaking or reasoning" (also "of or pertaining to speech"), from logos "reason, idea, word" (see Logos). Formerly also logick. Sometimes formerly plural, as in ethics, but this is not usual. Meaning "logical argumentation" is from c. 1600. Contemptuous logic-chopper "sophist, person who uses subtle distinctions in argument" is from 1846.
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."