line-sight

line of sight

noun
1.
Also called line of sighting. an imaginary straight line running through the aligned sights of a firearm, surveying equipment, etc.
2.
Astronomy. an imaginary line from an observer to a celestial body, coincident with the path traveled by light rays receivedfrom the body.
3.
Radio. a straight line connecting two points sufficiently high and near one another so that the line is entirely above the surface of the earth.
4.
Ophthalmology, line of vision.

Origin:
1550–60

Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
line of sight
 
n
1.  the straight line along which an observer looks or a beam of radiation travels
2.  ophthalmol another term for line of vision

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