evacuation (n.)

1520s (trans.), from Latin evacuatus, past participle of evacuare "to empty, make void, nullify," used by Pliny in reference to the bowels, used figuratively in Late Latin for "clear out;" from assimilated form of ex- "out" (see ex-) + vacuus "empty," from PIE *wak-, extended form of root *eue- "to leave, abandon, give out."

Earliest sense in English is medical. Military use is by 1710. Meaning "remove inhabitants to safer ground" is from 1934. Intransitive sense is from 1630s; of civilian persons by 1900. Replaced Middle English evacuen "draw off or expel (humors) from the body" (c. 1400). Related: Evacuated; evacuating.