"enter in a hostile manner," late 15c., from Latin invadere "to go, come, or get into; enter violently, penetrate into as an enemy, assail, assault, make an attack on," from in- "in" (from PIE root *en "in") + vadere "go, walk" (see vamoose). Compare evade. Related: invaded; invading.

mid-15c., invasioun, "an assault, attack, act of entering a country or territory as an enemy," from Old French invasion "invasion, attack, assault" (12c.), from Late Latin invasionem (nominative invasio) "an attack, invasion," noun of action from past-participle stem of Latin invadere "to go, come, or get into; enter violently, penetrate into as an enemy, assail, assault, make an attack on," from in- "in" (from PIE root *en "in") + vadere "to go, to walk, go hastily," from PIE root *wadh- (2) "to go" (source also of Old English wadan "to go," Latin vadum "ford;" see wade (v.)).

In extended sense, of diseases, "a harmful incursion of any kind;" with reference to rights, etc., "infringement by intrusion, encroachment by entering into or taking away what belongs to another."

c. 1300, "to start, initiate, cause to begin to be" (transitive), from Old French comencier "to begin, to start" (10c., Modern French commencer), from Vulgar Latin *cominitiare, originally "to initiate as priest, consecrate," from Latin com "with, together" (see com-) + initiare "to initiate," from initium "a beginning," literally "a going in," noun use of neuter past participle of inire "to go into, begin," from in- "into, in" (from PIE root *en "in") + ire "to go" (from PIE root *ei- "to go").

From late 14c. in intransitive sense "come into existence, begin to be," also "enter into a new state." Spelling with double -m- began in French and was established in English by 1500. Related: Commenced; commencing.

1560s, "go into camp, settle in temporary quarters," from en- (1) "make, put in" + camp (n.). Related: Encamped; encamping.

mid-15c., from Latin ingressus "an advance; walking; an entry," from ingress-, past participle stem of ingredi "to step into, enter," from in- "in" (from PIE root *en "in") + gradi "to step, go" (from PIE root *ghredh- "to walk, go"). The verb meaning "to enter, go in" sometimes said to be American English, but it is attested from early 14c.

also re-appearance, "a new appearing, another coming into view," 1660s, from re- "back, again" + appearance or else a noun formed to go with reappear.

in early use also engredient, early 15c., "something forming part of a mixture," from Latin ingredientem (nominative ingrediens) "that which enters into" (a compound, recipe, etc.), present participle of ingredi "go in, enter," from in- "in" (from PIE root *en "in") + gradi "to step, go" (from PIE root *ghredh- "to walk, go"). Also from early 15c. as an adjective, "forming part of a mixture."

"tending to invade, aggressive," mid-15c., invasif, from Old French invasif (15c.) or directly from Medieval Latin invasivus "invasive," from invas-, past-participle stem of invadere "go into; attack, invade," from in- "in" (from PIE root *en "in") + vadere "go, walk" (see vamoose).

c. 1600, Latin, literally "from the beginning," from ab "from" (see ab-) + ablative of initium "entrance, beginning," which is from or related to the verb inire "to go into, enter upon, begin" (see initial).

"a military advance," 1706, from Greek anabasis "military expedition," literally "a going up (from the coast)," especially in reference to the advance of Cyrus the Younger and his Greek mercenaries from near the Aegean coast into Asia, and the subsequent story of the retreat of the 10,000 narrated by Xenophon (401 B.C.E.). From anabainein "to go up, mount;" from ana "up" (see ana-) + bainein "to go, walk, step" (from PIE root *gwa- "to go, come"). Related: Anabatic.