Pencil of RaysAll the rays that issue from one point, or that can be focussed at one point (Latin, penicillus, little tail, whence penicillum, a painter's brush made of the hair of a cow's tail); so called because they are like the hairs of a paint-brush, except at the point where they aggregate. Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
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