calcium (n.)

Old English cealc "chalk, soft white limestone; lime, plaster; pebble," a West Germanic borrowing from Latin calx (2) "limestone, lime (crushed limestone), small stone," borrowed from Greek khalix "small pebble," which many trace to a PIE root for "split, break up," but Beekes writes that "There is no convincing etymology."

Cognate words in most Germanic languages still have the "limestone" sense, but in English transferred chalk to the opaque, white, soft limestone found abundantly in the south of the island. The modern spelling is from early 14c. The Latin word for "chalk" was creta, which also is of unknown origin. With many figurative or extended senses due to the use of chalk marks to keep tracks of credit for drinks in taverns and taprooms, or to keep the score in games.

word-forming element in chemistry, used to coin element names, from Latin adjectival suffix -ium (neuter of -ius), which formed metal names in Latin (ferrum "iron," aurum "gold," etc.). In late 18c chemists began to pay attention to the naming of their substances with words that indicate their chemical properties. Berzelius in 1811 proposed forming all element names in Modern Latin. As the names of some recently discovered metallic elements already were in Latin form (uranium, chromium, borium, etc.), the pattern of naming metallic elements in -ium or -um was maintained (in cadmium, lithium, plutonium, etc.; helium is an anomaly).