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ultrasonics
ultrasonogram
ultrasonography
ultrasound
ultrastructure
ultraviolet
ultraviolet astronomy
ultraviolet-visible spectroscopy
ultravirus
ulu
ululate
Uluru
Ulysses
um
Umayyad
umbel
umbelliferous
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umbra

um·bra [ úmbrə ] (plural um·bras or um·brae [ úmbree ])


noun 
Definition:
 
1. physics complete shadow: an area of complete shadow caused by light from all points of a source being prevented from reaching the area, usually by an opaque object

2. astronomy darkest part on moon or Earth: the darkest portion of the shadow cast by an astronomical object during an eclipse, especially that cast on Earth during a solar eclipse

3. astronomy dark part of sunspot: the inner, darker area of a sunspot

[Late 16th century. < Latin, "shadow"]

um·bral adjective
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