Etymology
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introduction (n.)

late 14c., "act of bringing into existence," from Old French introduccion (14c.) and directly from Latin introductionem (nominative introductio) "a leading in," noun of action from past-participle stem of introducere "to lead in, bring in; introduce; found, establish; bring forward (as an assertion)," from intro- "inward, to the inside" (see intro-) + ducere "to lead" (from PIE root *deuk- "to lead").

Meanings "initial instruction in a subject" and "an introductory statement" are from mid-15c.; meaning "elementary treatise on some subject" is from 1520s. The sense of "formal presentation of one person to another" is from 1711.

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reintroduction (n.)

also re-introduction, "a repeated or renewed introduction," 1660s, from re- "back, again" + introduction.

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introductory (adj.)
c. 1600, from Late Latin introductorius, from introduct-, past participle stem of Latin introducere "to lead in, bring in" (see introduction). Also used in English from c. 1400 as a noun meaning "introductory treatise or textbook."
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introduce (v.)

early 15c., "convey or bring (something) in or into," a back-formation from introduction or else from Latin introducere "to lead in, bring in," from intro- "inward, to the inside" (see intro-) + ducere "to lead" (from PIE root *deuk- "to lead").

Meaning "to bring forward, open to notice" (of a subject, etc.) is from 1550s. Sense of "bring into personal acquaintance, make known" (as of one person to another) is from 1650s. Related: Introduced; introducing.

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*deuk- 
Proto-Indo-European root meaning "to lead."

It forms all or part of: abduce; abducent; abduct; abduction; adduce; aqueduct; circumduction; conduce; conducive; conduct; conductor; conduit; deduce; deduction; dock (n.1) "ship's berth;" doge; douche; ducal; ducat; Duce; duchess; duchy; duct; ductile; duke (n.); educate; education; induce; induction; introduce; introduction; misconduct; produce; production; reduce; reduction; seduce; seduction; subduce; subduction; taut; team (n.); teem (v.1) "abound, swarm, be prolific;" tie (n.); tow (v.); traduce; transducer; tug; zugzwang.

It is the hypothetical source of/evidence for its existence is provided by: Latin dux (genitive ducis) "leader, commander," in Late Latin "governor of a province," ducere "to lead;" Old English togian "to pull, drag," teonteon "to pull, drag;" German Zaum "bridle," ziehen "to draw, pull, drag;" Middle Welsh dygaf "I draw."
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*en 
Proto-Indo-European root meaning "in."

It forms all or part of: and; atoll; dysentery; embargo; embarrass; embryo; empire; employ; en- (1) "in; into;" en- (2) "near, at, in, on, within;" enclave; endo-; enema; engine; enoptomancy; enter; enteric; enteritis; entero-; entice; ento-; entrails; envoy; envy; episode; esoteric; imbroglio; immolate; immure; impede; impend; impetus; important; impostor; impresario; impromptu; in; in- (2) "into, in, on, upon;" inchoate; incite; increase; inculcate; incumbent; industry; indigence; inflict; ingenuous; ingest; inly; inmost; inn; innate; inner; innuendo; inoculate; insignia; instant; intaglio; inter-; interim; interior; intern; internal; intestine; intimate (adj.) "closely acquainted, very familiar;" intra-; intricate; intrinsic; intro-; introduce; introduction; introit; introspect; invert; mesentery.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit antara- "interior;" Greek en "in," eis "into," endon "within;" Latin in "in, into," intro "inward," intra "inside, within;" Old Irish in, Welsh yn, Old Church Slavonic on-, Old English in "in, into," inne "within, inside."
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propaedeutic (n.)

"an introduction to an art or science," 1798, from Greek propaideuein "to teach beforehand," from pro "before" (see pro-) + paideuein "to teach," from pais (genitive paidos) "child" (see pedo-). By 1849 as an adjective, "pertaining to the introduction to any art or science."

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non-invasive (adj.)

also noninvasive, "not tending to spread; not require the introduction of instruments into the body," by 1850, from non- + invasive.

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Han 
Chinese dynasty, 206 B.C.E.-220 C.E., its rule was marked by prosperity, military success, and the introduction of Buddhism.
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