Meaning "net-wire frame used in windows and doors" is recorded from 1859. Meaning "flat vertical surface for reception of projected images" is from 1810, originally in reference to magic lantern shows; later of movies. Transferred sense of "cinema world collectively" is attested from 1914; hence screen test (1918), etc. Screen saver first attested 1990. Screen printing recorded from 1918.
"cylindrical body of tallow, wax, etc., formed on a wick and used as a source of artificial light," Old English candel "lamp, lantern, candle," an early ecclesiastical borrowing from Latin candela "a light, torch, candle made of tallow or wax," from candere "to shine," from PIE root *kand- "to shine."
The Latin word is also the source of French chandelle, Spanish candela, Irish coinneal, Welsh canwyll, Russian kandilo, Arabic qandil, etc. Candles were unknown in ancient Greece (where oil lamps sufficed), but common from early times among Romans and Etruscans. Candles on birthday cakes seem to have been originally a German custom. To hold a candle to originally meant "to help in a subordinate capacity," from the notion of an assistant or apprentice holding a candle for light while the master works (compare Old English taporberend "acolyte"). To burn the candle at both ends "consume or waste prodigiously" is recorded from 1730.
a red light as a sign to stop is from 1849, long before traffic signals; see red (adj.1) + light (n.). As the name of a children's game (in reference to the traffic light meaning) it is recorded from 1953.
The use of red-light district to indicate a city district with many brothels is by 1896.
On a few blocks east of the Bowery, in what was known as the Red Light district, there are still a few houses of this character. The Red Light district was so called because the hall light in disreputable houses had a red globe or shone through red curtains covering the transom of the hall door. A red light before a cigar store, cider room or coffee room indicated its purpose. The Parisian licensed brothel has a red lantern with the number of the house over the door. [I.L. Nascher, M.D., "The Wretches of Povertyville," Chicago, 1909]
"fantastic series or medley of illusive or terrifying figures or images," 1802, the name of a magic lantern exhibition brought to London in 1802 by Parisian showman Paul de Philipstal. The name is an alteration of French phantasmagorie, which is said to have been coined 1801 by French dramatist Louis-Sébastien Mercier as though to mean "crowd of phantoms," from Greek phantasma "image, phantom, apparition" (from PIE root *bha- (1) "to shine").
The second element appears to be a French form of Greek agora "assembly. "But the inventor of the word prob. only wanted a mouth-filling and startling term, and may have fixed on -agoria without any reference to the Greek lexicon" [OED]. The transferred meaning "shifting scene of many elements" is attested from 1822. Related: Phantasmagorical.
In Philipstal's 'phantasmagoria' the figures were made rapidly to increase and decrease in size, to advance and retreat, dissolve, vanish, and pass into each other, in a manner then considered marvellous. [OED]
fifteenth letter of the alphabet, from a character that in Phoenician was called 'ain (literally "eye") and represented "a very peculiar and to us unpronounceable guttural" [Century Dictionary]. The Greeks also lacked the sound, so when they adopted the Phoenician letters they arbitrarily changed O's value to a vowel. (Thus there is no grounds for the belief that the form of the letter represents the shape of the mouth in pronouncing it.) The Greeks later added a special character for "long" O (omega), and the original became "little o" (omicron).
In Middle English and later colloquial use, o or o' can be an abbreviation of on or of, and is still literary in some words (o'clock, Jack-o'-lantern, tam-o'-shanter, cat-o'-nine-tails, will-o'-the-wisp, etc.).
O' the common prefix in Irish surnames is from Irish ó, ua (Old Irish au, ui) "descendant."
The "connective" -o- is the usual connecting vowel in compounds taken or formed from Greek, where it often is the vowel in the stem. "[I]t is affixed, not only to terms of Greek origin, but also to those derived from Latin (Latin compounds of which would have been formed with the L. connecting or reduced thematic vowel, -i), especially when compounds are wanted with a sense that Latin composition, even if possible, would not warrant, but which would be authorized by the principles of Greek composition." [OED]
As "zero" in Arabic numerals it is attested from c. 1600, from the similarity of shape. Similarly the O blood type (1926) was originally "zero," denoting the absence of A and B agglutinogens.
As a gauge of track in model railroads, by 1905. For o as an interjection of fear, surprise, joy, etc., see oh.
The use of the colloquial or slang -o suffix in wino, ammo, combo, kiddo, the names of the Marx Brothers, etc., "is widespread in English-speaking countries but nowhere more so than in Australia" [OED].