"pertaining to the ancient Roman mile," 1640s, from Latin milliarius, from mille (see mile (n.)). As a noun, "a milestone," c. 1600, from Latin milliarium.
1630s, "the 1,000-year period of Christ's anticipated rule on Earth" (Revelation xx.1-5); from Modern Latin millennium, from Latin mille "thousand" (see million) + annus "year" (see annual); formed on analogy of biennium, triennium, etc. For vowel change, see biennial. General (non-theological) sense of "an aggregate of 1,000 years, a period or interval of 1,000 years" is attested by 1711. Meaning "the year 2000 A.D." is attested by 1970.
[T]he men of the modern world—up to a generation ago anyway—saw 2000 as a millennial year in the light of science. Men were then to be freed of want, misery, and disease; reason and advanced technology would rule; all would finally be for the best in what would then be the undoubted best of all possible worlds. [Bulletin of the Atomic Scientists, December 1962]
type of cereal grain known from antiquity and cultivated in warm regions, early 15c. (late 14c. as mile), from Old French millet, millot, diminutive of mil "millet," from Latin milium "millet," from PIE root *mele- "to crush, grind." Cognate with Greek meline, Lithuanian malnos (plural) "millet."
also millepede, type of many-legged hard-shelled arthropod, c. 1600, from Latin millepeda "wood louse," a type of crawling, insect-like arthropod, from mille "thousand" (see million) + pes (genitive pedis) "foot," from PIE root *ped- "foot." Probably a loan-translation of Greek khiliopous. The native name is thousand-legs. The number of legs is far from 1,000, though they are about twice as numerous as those of the centipede, but unlike some centipedes the millipede is quite harmless.