Etymology
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invasion (n.)
Origin and meaning of invasion

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."

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fencible (adj.)
early 15c., "capable of making a defense," short for defensible; also see fence (n.). As a noun, "soldier enlisted to defend against invasion and not liable to serve abroad" (1796).
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incursion (n.)
"hostile attack," early 15c., from Old French incursion "invasion, attack, assault" (14c.) or directly from Latin incursionem (nominative incursio) "a running against, hostile attack," noun of action from past participle stem of incurrere "run into or against, rush at" (see incur).
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Bernicia 
Anglo-Saxon kingdom in northernmost England, founded by mid-6c., eventually merged into Northumbria; the name evidently is a survival of a pre-invasion Celtic name, perhaps that represented by the Welsh Bryneich. Related: Berenician
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bridgehead (n.)
also bridge-head, 1801, "a fortification covering that end of a bridge which is most exposed to an enemy," from bridge (n.1) + head (n.). Compare French tête-de-pont. From 1930 as "advance point attained by a military force in the face of the enemy" (especially by invasion).
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sea-lion (n.)
c. 1600, "kind of lobster," from sea + lion. Later the name of a fabulous animal (in heraldry, etc.), 1660s. Applied from 1690s to various species of large eared seals. As code name for the planned German invasion of Britain, it translates German Seelöwe, announced by Hitler July 1940, scrubbed October 1940.
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Aztec 
"one of the native people who dominated the central highlands of Mexico in 1519 at the time of the Spanish invasion, 1787, from Spanish Azteca, from Nahuatl aztecatl (plural aztecah), meaning "coming from Aztlan," name of their legendary place of origin, usually said to lie somewhere in what is now southwestern U.S. Related: Aztecan.
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irruption (n.)

1570s, from French irruption (14c.) or directly from Latin irruptionem (nominative irruptio) "a breaking in, bursting in, invasion," noun of action from past-participle stem of irrumpere "to break in, force one's way in, burst into," from assimilated form of in- "into, in, on, upon" (from PIE root *en "in") + rumpere (see rupture (n.)). Frequently confused with eruption.

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intrusion (n.)
late 14c., "unjust invasion of property or usurpation of office," from Old French intrusion (14c.), from Medieval Latin intrusionem (nominative intrusio) "a thrusting in," noun of action from past participle stem of Latin intrudere "to thrust in, force in," from in- "in" (from PIE root *en "in") + trudere "to thrust, push," from PIE *treud- "to press, push, squeeze" (see threat).

Meaning "a thrusting or pushing in" is from 1590s; that of "act of intruding" is from 1630s. Geological sense is from 1816.
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kamikaze (n.)

"suicide flier," 1945, Japanese, literally "divine wind," from kami "god, providence" (see kami) + kaze "wind." Said to have been originally the name given in folklore to a typhoon which saved Japan from Mongol invasion by wrecking Kublai Khan's fleet (August 1281). The World War II attacks began in October 1944 off the Philippines. As an adjective from 1946.

As an aside, at war's end, the Japanese had, by actual count, a total of 16,397 aircraft still available for service, including 6,374 operational fighters and bombers, and if they had used only the fighters and bombers for kamikaze missions, they might have realized, additionally, 900 ships sunk or damaged and 22,000 sailors killed or injured. In fact, however, the Japanese had outfitted many aircraft, including trainers, as potential suicide attackers. As intelligence estimates indicated, the Japanese believed they could inflict at least 50,000 casualties to an invasion force by kamikaze attacks alone. [Richard P. Hallion, "Military Technology and the Pacific War," 1995]
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