ytterbium

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A soft, bright, silvery rare-earth element occurring in two allotropic forms and used as an x-ray source for portable irradiation devices, in some laser materials, and in some special alloys. Atomic number 70; atomic weight 173.04; melting point 824°C; boiling point 1,196°C; specific gravity 6.972 or 6.54 (25°C) depending on allotropic form; valence 2, 3. See Table at element.

Century Dictionary and Cyclopedia

1. n. In making the ‘glowers’ or filaments for the Nernst incandescent electric lamps it has been found that the mixture of zirconia with the earths of the yttria group gives the most satisfactory results when the latter contain a large proportion of ytterbium as compared with yttrium.
2. n. Chemical symbol, Yb; atomic weight, 173 (?). An element discovered by Marignac in gadolinite, in regard to which little is known. The spectrum of this metal is believed to be peculiar, and to justify its claim to be recognized as a distinct element.

Wiktionary

1. n. A metallic chemical element (symbol Yb) with an atomic number of 70.

GNU Webster's 1913

1. n. (Chem.) A rare element of the boron group, sometimes associated with yttrium or other related elements, as in euxenite and gadolinite. Symbol Yb; provisional atomic weight 173.2. Cf. yttrium.

WordNet 3.0

1. n. a soft silvery metallic element; a rare earth of the lanthanide series; it occurs in gadolinite and monazite and xenotime