Progress in science and industry is constantly demanding new terms and one of the latest of these is the word "decibel," coined by telephone engineers to describe the efficiency of telephone circuits. It is a substitute for the phrase "transmission unit." The actual unit decided upon was first called "bel," after the inventor of the telephone. The bel, however, is larger than is needed in practice, and, therefore, a unit one-tenth as large was adopted by engineers and named the decibel. [Popular Mechanics, May 1929]
unit of the metric system for solid measure, 1798, from French stère "unit of volume equal to one cubic meter," from Greek stereos "solid, stiff, firm" (from PIE root *ster- (1) "stiff"). Little used, cubic meter generally serving instead.
unit of molecular quantity, 1902, from German Mol coined 1900 by German chemist Wilhelm Ostwald, short for Molekül (see molecule).
1918, "x-ray dose unit," a shortened form of radiation (q.v.). The meaning "unit of absorbed dose of ionizing radiation" is by 1954, an acronym from radiation absorbed dose. As shortened form of radical (n.), it is attested in political slang from 1820. Teen slang adjectival sense of "extraordinary, wonderful" is from late 1970s (see radical (adj.)).