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penumbra

Pronunciation: pe-num'bra

Definition: The region of partial illumination or radiation caused by light or x-rays not originating from a point source; also called geometric unsharpness.

[Mod. L., fr. L. paene, almost, + umbra, shadow]

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© Copyright 2018 Wolters Kluwer. All Rights Reserved. Review date: Sep 19, 2016.

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