Length is a measurement of how long something is in time or space. You can measure the length of a table or the length of a movie.

If an object has multiple distances to be measured (like a rectangle for example), then length is taken to be the longest of the measurements (as opposed to the width, in the case of the rectangle). Before babies learn to walk, they are measured for length, but once they begin to stand reliably the same measurement changes names, and become height.

Definitions of length

n the linear extent in space from one end to the other; the longest dimension of something that is fixed in place

“the length of the table was 5 feet”
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the length of the closed curve of a circle
diam, diameter
the length of a straight line passing through the center of a circle and connecting two points on the circumference
r, radius
the length of a line segment between the center and circumference of a circle or sphere
the property of being of long spatial extent
the property of being of short spatial extent
the apparent radius of a celestial body when viewed as a disc from the earth
radius of curvature
the radius of the circle of curvature; the absolute value of the reciprocal of the curvature of a curve at a given point
bore, caliber, calibre, gauge
diameter of a tube or gun barrel
the space between the projectile of a smoothbore gun and the surface of the bore of the gun
extension, lengthiness, prolongation
amount or degree or range to which something extends
the quality of being elongated
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physical property
any property used to characterize matter and energy and their interactions
the magnitude of something in a particular direction (especially length or width or height)
fundamental measure, fundamental quantity
one of the four quantities that are the basis of systems of measurement

n size of the gap between two places

“he determined the length of the shortest line segment joining the two points”
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(nautical) the distance traveled by a sailing vessel on a single tack
arm's length
a distance sufficient to exclude intimacy
the distance between the rails of a railway or between the wheels of a train
light time
distance measured in terms of the speed of light (or radio waves)
skip distance
the shortest distance that permits radio signals (of a given frequency) to travel from the transmitter to the receiver by reflection from the ionosphere
wingspan, wingspread
linear distance between the extremities of an airfoil
distance between the tips of the wings (as of a bird or insect) when fully extended
the perpendicular distance from the base of a geometric figure to the opposite vertex (or side if parallel)
broad gauge
a railroad track (or its width) broader than the standard 56.5 inches
narrow gauge
a railroad track (or its width) narrower than the standard 56.5 inches
standard gauge
railroad track having the standard width of 56.5 inches
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the physical magnitude of something (how big it is)

n a section of something that is long and narrow

“a length of timber”
“a length of tubing”
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section, segment
one of several parts or pieces that fit with others to constitute a whole object

n continuance in time

“he complained about the length of time required”
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duration as an extension
continuation, lengthiness, prolongation, protraction
the consequence of being lengthened in duration
the property of being (or seeming to be) without end
the property of being of short temporal extent
brevity, briefness, transience
the attribute of being brief or fleeting
permanence, permanency
the property of being able to exist for an indefinite duration
impermanence, impermanency
the property of not existing for indefinitely long durations
length of service, longevity
duration of service
(music) a prolongation of unspecified length on a note or chord or rest
ceaselessness, continuousness, incessancy, incessantness
the quality of something that continues without end or interruption
perpetuity, sempiternity
the property of being perpetual (seemingly ceaseless)
durability, enduringness, lastingness, strength
permanence by virtue of the power to resist stress or force
imperishability, imperishableness, imperishingness
the property of being resistant to decay
the property of being extremely durable
the property of lasting only a short time
transience, transiency, transitoriness
an impermanence that suggests the inevitability of ending or dying
the quality or state of being mortal
the quality or state of being immortal
the temporal property of being cut short
the temporal property of being very short
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temporal property
a property relating to time

n the property of being the extent of something from beginning to end

“the editor limited the length of my article to 500 words”
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the distance or area or volume over which something extends