"articles of (women's) clothing that may be worn in various combinations," 1945, from separate (adj.). Earlier, in the publishing trade, the word meant "printed article or document issued separately, for distribution, from the volume of which it forms a part" (1886). As a noun, separate is attested from 1610s in the sense "separatist."
word-forming element meaning "small in size or extent, microscopic; magnifying;" in science indicating a unit one millionth of the unit it is prefixed to; from Latinized form of mikros, Attic form of Greek smikros "small, little, petty, trivial, slight," perhaps from PIE *smika, from root *smik- "small" (source also of Old High German smahi "littleness"), but Beekes thinks it a Pre-Greek word.
"a filtration unit of the kidney," 1932, from German nephron (1924), from Greek nephros "kidney" (see nephro-).
1550s, "pertaining to astronomy," from astronomy + -ical. The popular meaning "immense, concerning very large figures" (as sizes and distances in astronomy) is attested from 1899. Astronomical unit (abbreviation A.U.) "mean distance from the Earth to the Sun," used as a unit of measure of distance in space, is from 1909. Related: Astronomically.
unit of force, 1904, named in honor of Sir Isaac Newton (1642-1727). Related: Newtonian.
also R.E.M., rem, unit for measuring ionizing radiation, 1947, acronym of roentgen equivalent man.