A silvery-white, brittle, nonmetallic chemical element of crystalline structure, found only in combination. It is used in alloys with metals to harden them and increase their resistance to chemical action. Compounds of antimony are used in medicines, pigments, and matches, and for fireproofing.

Symbol: Sb (Latin: stibium)
Atomic number: 51
Atomic weight: 121.76
Density (at room temperature and pressure): 6.91 g/cc
Melting point: 630.63°C
Boiling point: 1,587°C
Main valence: -3, +3, +5
Ground state electron configuration: [Kr]4d105s25p3

Etymologically, "antimony" is from the Medieval Latin antimonium, used by Constantinus Africanus of Salerno (Chaucer's "cursed monk, daun Constantyn" in The Merchant's Tale, line 566) at the end of the eleventh century. The word is of unknown origin. Some have analyzed the French antimoine as anti- + moine, "against the monks" and supported this derivation by an idle tale in which the chemist Basil Valentine poisons several monks using antimony at the end of the fifteenth century. However, this story makes the name originate over four hundred years later than a known usage of it.