Invade is defined as to enter using force or violence, or to crowd into a place.(verb)
An example of to invade is the 1939 Defensive War when Nazi Germany entered Poland from the north, south and west.
See invade in Webster's New World College Dictionary
Origin: ME invaden < L invadere < in-, in + vadere, to come, go: see wade
See invade in American Heritage Dictionary 4
verb in·vad·ed, in·vad·ing, in·vades verb, transitive
Origin: Middle English
Origin: , from Old French invader
Origin: , from Latin invādere
Origin: : in-, in; see in-2
Origin: + vādere, to go.
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