a salt of hydrocyanic acid, 1826, from cyan-, used in science as a word-forming element for the carbon-nitrogen compound radical, + chemical ending -ide, on analogy of chloride. The best-known is potassium cyanide, bitter-tasting and extremely poisonous but formerly used in photography, electro-metallurgy, etc.
1690s, originally an art criticism term, "assemblage of figures or objects forming a harmonious whole in a painting or design," from French groupe "cluster, group" (17c.), from Italian gruppo "group, knot," which probably is, with Spanish grupo, from a Germanic source, from Proto-Germanic *kruppaz "round mass, lump," part of the general group of Germanic kr- words with the sense "rounded mass" (such as crop (n.).
Extended to "any assemblage, a number of individuals related in some way" by 1736. Meaning "pop music combo" is from 1958. As it was borrowed after the Great Vowel Shift in English, the pronunciation of the -ou- follows French rather than English models.
"photograph picture obtained by the use of cyanide," 1842, from cyan- + ending from daguerreotype (see type (n.)).
"act, process, or result of arranging in a group," 1748, verbal noun from group (v.).
type of fumigant used to kill rats in enclosed spaces, such as holds of ships, boxcars, etc., 1926, from German Zyklon, commercial name of a type of hydrogen cyanide, said to be of unknown etymology, but it is the usual German form of the word cyclone. There were at least three varieties, A, B, and C, Zyklon-B being the one notoriously used in the Nazi death camps.