late 14c., "gaping void; empty, immeasurable space," from Old French chaos (14c.) or directly from Latin chaos, from Greek khaos "abyss, that which gapes wide open, that which is vast and empty," from *khnwos, from PIE root *ghieh- "to yawn, gape, be wide open."
Meaning "utter confusion" (c. 1600) is an extended sense from theological use of chaos in the Vulgate version of "Genesis" (1530s in English) for "the void at the beginning of creation, the confused, formless, elementary state of the universe." The Greek for "disorder" was tarakhe, but the use of chaos here was rooted in Hesiod ("Theogony"), who describes khaos as the primeval emptiness of the Universe, and in Ovid ("Metamorphoses"), who opposes Khaos to Kosmos, "the ordered Universe." Sometimes it was personified as a god, begetter of Erebus and Nyx ("Night").
Meaning "orderless confusion" in human affairs is from c. 1600. Chaos theory in the modern mathematical sense is attested from c. 1977.
"destitute, not possessing, lacking" (with of), c. 1400, shortening of devoided, past participle of obsolete Middle English verb devoiden "to remove, void, vacate" (c. 1300), from Old French desvuidier (12c., Modern French dévider) "to empty out, flush game from, unwind, let loose (an arrow)," from des- "out, away" (see dis-) + voider "to empty," from voide "empty," from Latin vocivos "unoccupied, vacant," related to vacare "be empty," from PIE *wak-, extended form of root *eue- "to leave, abandon, give out."
early 13c., "white, pale, colorless," from Old French blanc "white, shining," from Frankish *blank "white, gleaming," or some other Germanic source (compare Old Norse blakkr, Old English blanca "white horse;" Old High German blanc, blanch; German blank "shining, bright"), from Proto-Germanic *blangkaz "to shine, dazzle," extended form of PIE root *bhel- (1) "to shine, flash, burn," also "shining white."
Meaning "having empty spaces" evolved c. 1400. Sense of "void of expression" (a blank look) is from 1550s. Spanish blanco, Italian bianco are said to be from Germanic. Related: Blankly, blankness.
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.