source: By Pearson Scott Foresman - Archives of Pearson Scott Foresman, donated to the Wikimedia Foundation, Public Domain

1. an imaginary line about which a body rotates:

(回転体の)軸; (地球の)地軸(→ globe)

e.g. the Earth revolves on its axis once every 24 hours.

Geometry an imaginary straight line passing through the center of a symmetrical solid, about which a plane figure can be conceived as rotating to generate the solid.

an imaginary line which divides something into equal or roughly equal halves, especially in the direction of its greatest length.

(平面を等分する)中心線

2. Mathematics a fixed reference line for the measurement of coordinates:

(グラフの)軸

e.g. the variable that is thought of as a cause is placed on the horizontal axis, and the variable that is thought of as an effect on the vertical axis.

3. a straight central part in a structure to which other parts are connected.

Botany the central column of an inflorescence or other growth:

e.g. the leaflets are arranged in rows on a slender axis.

Zoology the skull and backbone of a vertebrate animal.

4. Anatomy the second cervical vertebra, below the atlas at the top of the backbone.

5. an agreement or alliance between two or more countries that forms a center for an eventual larger grouping of nations:

〖通例単数形で〗(国家間の)枢軸(alliance)

e.g. the Anglo-American axis.

(the Axis) the alliance of Germany and Italy formed before and during World War II, later extended to include Japan and other countries:

〖the A-〗(第2次大戦での)枢軸国〘独と伊; のちに日本などが加わる; → ally〙

e.g. as modifier : the Axis Powers.

late Middle English: from Latin, ‘axle, pivot’.