tantalum

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A very hard, dense, gray metallic element that occurs chiefly in columbite-tantalite and is exceptionally resistant to chemical attack below 150°C. It is used to make electrolytic capacitors for portable electronic and computing devices; superalloys for aircraft, missile, and nuclear reactor parts; filaments; and surgical instruments. Atomic number 73; atomic weight 180.948; melting point 3,017°C; boiling point 5,458°C; specific gravity 16.4; valence 2, 3, 4, 5. cross-reference: Periodic Table.

from The Century Dictionary.

• noun 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.
• noun 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.

from the GNU version of the Collaborative International Dictionary of English.

• noun (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.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A metallic chemical element (symbol Ta) with an atomic number of 73.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a hard grey lustrous metallic element that is highly resistant to corrosion; occurs in niobite and fergusonite and tantalite