tantalum

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A very hard, heavy, gray metallic element that is exceptionally resistant to chemical attack below 150°C. It is used to make light-bulb filaments, electrolytic capacitors, lightning arresters, nuclear reactor parts, and some surgical instruments. Atomic number 73; atomic weight 180.948; melting point 2,996°C; boiling point 5,425°C; specific gravity 16.6; valence 2, 3, 4, 5. See Table at element.

Century Dictionary and Cyclopedia

1. n. Knowledge of this metal has been much increased by recent research. Brought to the elementary state by heating together sodium and an alkaline tantalofluoride and fused in an electric furnace, it appears as a solid of grayish-white color and metallic luster, like platinum, of specific gravity 16.64. It combines in a most remarkable way intense hardness with a high degree of ductility, so that it can be drawn into wire.05 millimeters in diameter having a resisting tensile stress ranging up to 93 kilos., or for fine wire 150 or 160 kilos., per square millimeter before breaking. It melts at 2,250–2,300° C., resists all the ordinary acids and alkaline solutions, is attacked by hydrofluoric acid and by fused caustic alkalis, and as thin wire bums, when heated in oxygen, with a bright white light.
2. n. Chemical symbol, Ta; atomic weight, 192. One of the rare metals occurring in various combinations, but hardly known at all in the separate metallic state. As prepared by Berzelius, but not entirely pure, it appeared as a black powder, which assumed a grayish metallic luster under the burnisher, and which when gently heated took fire, and burned to an oxid. It was discovered by Ekeberg, in 1802, in the mineral afterward named by him yttrotantalite, and it has since been found in various rare minerals, as tantalite, columbite, pyrochlore, fergusonite, etc., in which it is almost always associated with niobium. It also occurs in small quantities in various tin, tungsten, and uranium ores. In its chemical relations it is allied to bismuth, antimony, and niobium.

Wiktionary

1. n. A metallic chemical element (symbol Ta) with an atomic number of 73.

GNU Webster's 1913

1. n. (Chem.) A rare nonmetallic element found in certain minerals, as tantalite, samarskite, and fergusonite, and isolated as a dark powder which becomes steel-gray by burnishing. Symbol Ta. Atomic weight 182.0. Formerly called also tantalium.

WordNet 3.0

1. n. a hard grey lustrous metallic element that is highly resistant to corrosion; occurs in niobite and fergusonite and tantalite