axis

The definition of an axis is a real or imaginary line on which something rotates, or a straight line around which things are evenly arranged.

(noun)

An example of axis is an imaginary line running through the earth on which the earth rotates.
An example of axis is the line running through the body from head to feet determining left and right sides.

See axis in Webster's New World College Dictionary

noun pl. axes

a real or imaginary straight line on which an object rotates or is regarded as rotating: the axis of a planet
a real or imaginary straight line around which the parts of a thing, system, etc. are symmetrically or evenly arranged or composed: the axis of a picture
a main line of motion, development, etc.
an alignment between countries, groups, etc. for promoting their purposes
Aeron. any of the three straight lines, perpendicular to each other, passing through the center of gravity of an aircraft, namely the longitudinal axis from nose to tail, the lateral axis from side to side, and the vertical axis from above to below
Anat.
1. the second cervical vertebra
2. any of various axial or central parts
Bot.
1. the main stem of a plant
2. the central system of a cluster
Geom.
1. a straight line through the center of a plane figure or solid, esp. one around which the parts are symmetrically arranged
2. a straight line for measurement or reference, as in a graph
Optics
1. a straight line through the centers of both surfaces of a lens
2. a straight line from the object of vision to the fovea of the eye

Origin: L, axle, axis < IE *aks- < base *aĝ- (see act) > OE eax, ON ǫxull, Gr axōn, L axilla

noun

any of a genus (Axis) of small deer of India and S Asia, with slender, sparsely branched antlers

Origin: ModL < L

See axis in American Heritage Dictionary 4

noun pl. ax·es (ăkˈsēzˌ)

A straight line about which a body or geometric object rotates or may be conceived to rotate.
Mathematics
a. An unlimited line, half-line, or line segment serving to orient a space or a geometric object, especially a line about which the object is symmetric.
b. A reference line from which distances or angles are measured in a coordinate system.
A center line to which parts of a structure or body may be referred.
An imaginary line to which elements of a work of art, such as a picture, are referred for measurement or symmetry.
Anatomy
a. The second cervical vertebra on which the head turns.
b. Any of various central structures, such as the spinal column, or standard abstract lines used as a positional referent.
Botany The main stem or central part about which organs or plant parts such as branches are arranged.
One of three mutually perpendicular lines that define the orientation of an aircraft, with one being along its direction of travel and the other two being perpendicular to the direction of travel.
A line through the optical center of a lens that is perpendicular to both its surfaces.
One of three or four imaginary lines used to define the faces of a crystal and the position of its atoms.
a. An alliance of powers, such as nations, to promote mutual interests and policies.
b. Axis The alliance of Germany and Italy in 1936, later including Japan and other nations, that opposed the Allies in World War II.