axis

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A straight line about which a body or geometric object rotates or may be conceived to rotate.
2. n. Mathematics 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.
3. n. Mathematics A reference line from which distances or angles are measured in a coordinate system.
4. n. A center line to which parts of a structure or body may be referred.
5. n. An imaginary line to which elements of a work of art, such as a picture, are referred for measurement or symmetry.
6. n. Anatomy The second cervical vertebra on which the head turns.
7. n. Anatomy Any of various central structures, such as the spinal column, or standard abstract lines used as a positional referent.
8. n. Botany The main stem or central part about which organs or plant parts such as branches are arranged.
9. n. 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.
10. n. A line through the optical center of a lens that is perpendicular to both its surfaces.
11. n. One of three or four imaginary lines used to define the faces of a crystal and the position of its atoms.
12. n. An alliance of powers, such as nations, to promote mutual interests and policies.
13. n. The alliance of Germany and Italy in 1936, later including Japan and other nations, that opposed the Allies in World War II.

Century Dictionary and Cyclopedia

1. n. The motionless, or relatively motionless, imaginary line about which a rotating body, such as the earth, turns: specifically called in this sense the axis of revolution or rotation (which see, below).
2. n. The axle of a wheel; the cylindrical portion of any mechanical piece intended to turn in bearings: as, the axis of a transit instrument.
3. n. In anatomy: The second cervical vertebra: so called because the atlas turns upon it as about a pivot or axis, bearing the head with it.
4. n. It is usually distinguished from the other vertebræ by having an odontoid or tooth-like process, furnishing the pivot about which the atlas turns: hence called the toothed vertebra (vertebra dentata), or the odontoid vertebra (vertebra odontoidea).
5. n. The odontoid process of the axis.
6. n. The entire vertebral column.
7. n. The central or axial nervous system of a vertebrate: as, the cerebrospinal axis.
8. n. The columella or modiolus of the cochlea.
9. n. A short thick artery which immediately divides into several branches: as, the celiac axis; the thyroid axis.
10. n. The axis-cylinder of a nerve.
11. n. Same as axon.
12. n. The central line of a solid of revolution; the central line of any symmetrical, or nearly symmetrical, body: as, the axis of a cylinder, of the eye, etc.
13. n. Any line with reference to which the physical properties of a body, especially its elasticity, are symmetrical.
14. n. In Trilobita, specifically, the tergum; the median convex portion of a thoracic somite, intervening between the pleura or flattened lateral portions of the thorax. See cut under Trilobita.
15. n. In conchology, the imaginary line or space around which the whorls of a spiral shell turn.
16. n. In botany, the stem; the central part or longitudinal support on which organs or parts are arranged. The root has sometimes been called the descending axis.
17. n. In geography and geology, the central or dominating region of a mountain-chain, or the line which follows the crest of a range and thus indicates the position of the most conspicuous portion of the uplift. In a folded region, or one in which the strata have been bent into anticlinals and synclinals, the axis of each fold is the plane indicating the direction parallel to which the folding has taken place, or toward which the strata incline.
18. n. In analytical geometry, any fixed line of reference used to determine the position of a point or series of points (line, surface) in space.
19. n. A kind of East Indian deer, Cervus axis, of which there are several varieties, perhaps species. The body is spotted with white. Also called axis-deer, spotted deer, and hog-deer.
20. n. 2. [capitalized] [NL.] A genus of such deer.
21. n. In architecture, one of several lines, either imagined or laid down in the plans, etc., which pass through the middle of an important feature. Thus the axis of an entrance-hall will probably be carried through the middle of the outer doorway, the vestibule and inner doorway, and the hall proper. In symmetrical planning and designing the parts on one side of the axis are exactly like those on the other side. Any feature, as a door or a window, may or may not be on the axis. Compare en axe.
22. n. of a lens, any straight line through the center of the lens which does not coincide with the radii of curvature. (Used only in the approximate theory of lenses, in which the thickness is ignored.)

Wiktionary

1. n. geometry An imaginary line around which an object spins (an axis of rotation) or is symmetrically arranged (an axis of symmetry).
2. n. mathematics A fixed one-dimensional figure, such as a line or arc, with an origin and orientation and such that its points are in one-to-one correspondence with a set of numbers; an axis forms part of the basis of a space or is used to position and locate data in a graph (a coordinate axis).
3. n. anatomy The second cervical vertebra of the spine.
4. n. Axis axis, a deer native to Asia.

GNU Webster's 1913

1. n. (Zoöl.) The spotted deer (Cervus axis or Axis maculata) of India, where it is called hog deer and parrah (Moorish name).
2. n. A straight line, real or imaginary, passing through a body, on which it revolves, or may be supposed to revolve; a line passing through a body or system around which the parts are symmetrically arranged.
3. n. (Math.) A straight line with respect to which the different parts of a magnitude are symmetrically arranged
4. n. (Bot.) The stem; the central part, or longitudinal support, on which organs or parts are arranged; the central line of any body.
5. n. The second vertebra of the neck, or vertebra dentata.
6. n. Also used of the body only of the vertebra, which is prolonged anteriorly within the foramen of the first vertebra or atlas, so as to form the odontoid process or peg which serves as a pivot for the atlas and head to turn upon.
7. n. (Crystallog.) One of several imaginary lines, assumed in describing the position of the planes by which a crystal is bounded.
8. n. (Fine Arts) The primary or secondary central line of any design.

WordNet 3.0

1. n. the main stem or central part about which plant organs or plant parts such as branches are arranged
2. n. a straight line through a body or figure that satisfies certain conditions
3. n. a group of countries in special alliance
4. n. the 2nd cervical vertebra; serves as a pivot for turning the head
5. n. the center around which something rotates
6. n. in World War II the alliance of Germany and Italy in 1936 which later included Japan and other nations