Origin and history of argon

late 14c., litarge, "state of prolonged torpor or inactivity, inertness of body or mind," from Medieval Latin litargia, from Late Latin lethargia, from Greek lēthargia "forgetfulness," from lēthargos "forgetful," apparently etymologically "inactive through forgetfulness," from lēthē "a forgetting, forgetfulness" (see latent) + argos "idle" (see argon). The form with -th- is from 1590s in English. The Medieval Latin word also is the source of Old French litargie (Modern French léthargie), Spanish and Italian letargia.

heavy, inert gaseous element, 1898, from Greek xenon, neuter of xenos "foreign, strange" (from PIE root *ghos-ti- "stranger, guest, host"); coined by its co-discoverer, Scottish chemist Sir William Ramsay (1852-1916). Compare krypton (kryptos "hidden") neon (neos "new"), argon (argos "idle") all allied and named during the same rush of discovery, but the names perhaps randomly distributed, as no suggestion is made that xenon is stranger or argon lazier than the others.

The announcement of the discovery of two new elements, Monium and Xenon, must constitute a record for the first two days of the meeting, although new elements, especially amongst the rarer earths and gases, hardly excite the interest that similar discoveries did some years back. ["Chemistry at the British Association," in Nature, Oct. 6, 1898. Monium turned out not to be an element.]