word-forming element meaning "under, beneath; behind; from under; resulting from further division," from Latin preposition sub "under, below, beneath, at the foot of," also "close to, up to, towards;" of time, "within, during;" figuratively "subject to, in the power of;" also "a little, somewhat" (as in sub-horridus "somewhat rough"), from PIE *(s)up- (perhaps representing *ex-upo-), a variant form of the root *upo "under," also "up from under." The Latin word also was used as a prefix and in various combinations.

In Latin assimilated to following -c-, -f-, -g-, -p-, and often -r- and -m-. In Old French the prefix appears in the full Latin form only "in learned adoptions of old Latin compounds" [OED], and in popular use it was represented by sous-, sou-; as in French souvenir from Latin subvenire, souscrire (Old French souzescrire) from subscribere, etc.

The original meaning is now obscured in many words from Latin (suggest, suspect, subject, etc.). The prefix is active in Modern English, sometimes meaning "subordinate" (as in subcontractor); "inferior" (17c., as in subhuman); "smaller" (18c.); "a part or division of" (c. 1800, as in subcontinent).

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."

1520s, "to persuade a vassal, etc., to desert his allegiance or service," from Latin seducere "lead away, lead aside or astray," from se- "aside, away" (see se-) + ducere "to lead" (from PIE root *deuk- "to lead"). The sexual sense, now the prevailing one, is attested from 1550s (it apparently was not in Latin), originally specifically "entice (a woman) to a surrender of chastity." Related: Seduced; seducing.

Caxton used seduisen (late 15c.), from Old French suduire "to corrupt, seduce" (Modern French séduire "seduce"), from Latin subducere "draw away, withdraw, remove" (see subduce).

1570s, "subtract," from Latin subductus, past participle of subducere "to draw away, take away" (see subduce). Geological sense is from 1971, a back-formation from subduction. Related: Subducted; subducting.

early 15c., "withdrawal, removal" (originally of noxious substances from the body), from Latin subductionem (nominative subductio) "a withdrawal, drawing up, hauling ashore," noun of action from past participle stem of subducere "to draw away, take away" (see subduce). Geological sense is attested from 1970, from French (1951).

late 14c., "to conquer and reduce to subjection," from Old French souduire, but this meant "deceive, seduce," from Latin subducere "draw away, lead away, carry off; withdraw" (see subduce). The primary sense in English seems to have been taken in Anglo-French from Latin subdere and attached to this word. Related: Subdued; subduing. As an associated noun, subdual is attested from 1670s (subduction having acquired other senses).