| pentylenetetrazole | <chemical> 6,7,8,9-tetrahydro-5h-tetrazolo(1,5-a)azepine. A convulsant used primarily in animal experiments. It was formerly used as a central nervous system stimulant. Pharmacological action: convulsants. Chemical name: 5H-Tetrazolo(1,5-a)azepine, 6,7,8,9-tetrahydro- (12 Dec 1998) |
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| penumbra | 1. An incomplete or partial shadow. 2. <astronomy> The shadow cast, in an eclipse, where the light is partly, but not wholly, cut off by the intervening body; the space of partial illumination between the umbra, or perfect shadow, on all sides, and the full light. The faint shade surrounding the dark central portion of a solar spot is also called the penumbra, and sometimes umbra. 3. The part of a picture where the shade imperceptibly blends with the light. Origin: NL, fr. L. Paene almost + umbra shade. Source: Websters Dictionary (01 Mar 1998) |
| penwoman | A female writer; an authoress. Source: Websters Dictionary (01 Mar 1998) |