mid-13c., from Medieval Latin elixir "philosopher's stone," believed by alchemists to transmute baser metals into gold and/or to cure diseases and prolong life, from Arabic al-iksir "the philosopher's stone," probably from late Greek xerion "powder for drying wounds," from xeros "dry" (see xerasia). Later in medical use for "a tincture with more than one base." General sense of "strong tonic" is 1590s; used for quack medicines from at least 1630s.

mid-15c., of a day, "clear, fair, calm," from Old French serein and directly from Latin serenus "peaceful, calm, clear, unclouded" (of weather); figuratively "cheerful, glad, tranquil"(from PIE root *ksero- "dry," source also of Greek xeros "dry, arid;" see xerasia).

In English, the word has been applied to persons, characters, etc. since 1630s: "tranquil, unruffled." Related: Serenely. Middle English also had serenous (mid-15c.), of places, "having clear, fair weather."

before vowels, xer-, word-forming element meaning "dry," from Greek xero-, combining form of xeros "dry, withered" (see xerasia).

"photographic reduplication without liquid developers," 1948, from Greek xeros "dry" (see xerasia) + -ography as in photography. Related: Xerographic.

Xerography: Inkless printing and dry photography—named "xerography," from the Greek words for "dry" and "writing"—were recently demonstrated in the United States. Described as "revolutionary" by the New York Times, xerography employs static electricity to record images on special metal plates, and dry powders to reproduce the images on other surfaces. [U.S. Department of State "Air Bulletin," No. 79, vol. 2, Nov. 17, 1948]

1890, Modern Latin, from Greek xerosis, from xeros "dry" (see xerasia) + -osis.