An axis is a straight line, sometimes seen, sometimes not, that is important in mathematics, art, science and our survival. The most famous axis is the one the earth spins around, giving us the 24-hour day.

In graphs, one side is usually the "X axis" and the other the "Y axis." Axis lines are also the lines that run through spheres, like our earth, around which those spheres rotate. In a totally different area, axis is used to describe countries in an alliance. During World War II, Germany, Japan, and Italy were known as the Axis Powers.

Definitions of axis
  1. noun
    a straight line through a body or figure that satisfies certain conditions
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    coordinate axis
    one of the fixed reference lines of a coordinate system
    major axis
    the longest axis of an ellipse or ellipsoid; passes through the two foci
    semimajor axis
    one-half the major axis of an ellipse; the distance from the center of an ellipse to one end
    minor axis
    the shorter or shortest axis of an ellipse or ellipsoid
    semiminor axis
    one-half the minor axis of an ellipse
    optic axis, principal axis
    a line that passes through the center of curvature of a lens so that light is neither reflected nor refracted
    optic axis
    in a doubly refracting crystal, the line in the direction of which no double refraction occurs
    the horizontal axis in a plane coordinate system
    the vertical axis in a plane coordinate system
    the third axis in a 3-dimensional coordinate system
    type of:
    a spatial location defined by a real or imaginary unidimensional extent
  2. noun
    the center around which something rotates
    synonyms: axis of rotation
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    pin, pivot
    axis consisting of a short shaft that supports something that turns
    rotor head, rotor shaft
    the axis around which the major rotor of a helicopter turns
    the pivot about which a lever turns
    a pin or bolt forming the pivot of a hinge
    type of:
    device consisting of a piece of machinery; has moving parts that perform some function
  3. noun
    the main stem or central part about which plant organs or plant parts such as branches are arranged
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    axis of a compound leaf or compound inflorescence
    the fleshy axis of a spike often surrounded by a spathe
    type of:
    stalk, stem
    a slender or elongated structure that supports a plant or fungus or a plant part or plant organ
  4. noun
    the 2nd cervical vertebra; serves as a pivot for turning the head
    synonyms: axis vertebra
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    type of:
    cervical vertebra, neck bone
    one of 7 vertebrae in the human spine located in the neck region
  5. noun
    a group of countries in special alliance
    synonyms: bloc
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    scheduled territories, sterling area, sterling bloc
    the group of countries whose currencies are tied to the British pound sterling
    type of:
    alignment, alinement, alliance, coalition
    an organization of people (or countries) involved in a pact or treaty
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