Period 3 element in 1810, who named it chlorine, from the Greek word χλωρος (chlōros), meaning "green-yellow." Chlorine is a component of various compounds, including table salt. It is the second most abundant halogen and 21st most abundant chemical element in Earth's crust. The great oxidizing potential of chlorine led it to its bleaching and disinfectant uses, as well as uses of an essential reagent in the chemical industry. As a common disinfectant, chlorine compounds are used in swimming pools to keep them clean and sanitary. In the upper atmosphere, chlorine-containing molecules such as chlorofluorocarbons have been implicated in ozone depletion. "Argon" (symbol
Tre- (place name element) was evidence of political and linguistic distinction at some time from the 8th to 11th centuries. Tre- (place name element) Tre- is a place name element of Celtic origin meaning "hamlet, farmstead, estate", etc. which survives mainly in Wales and in the Southwest of England (almost exclusively in Cornwall). The manor of Trefusis was thus originally held before the Norman Conquest of 1066 by an Anglo-Saxon named "Fusis" or similar, thus "Farmstead of Fusis". The Cornish place-name beginning "Tre-" may be compared to the Cornish place-name beginning "Bod-" and the place-name endings "-worthy" and "-cot" in Devon, and "-ham" and