Definitions of axis:

• noun:   the center around which something rotates
• noun:   the 2nd cervical vertebra; serves as a pivot for turning the head
• noun:   a straight line through a body or figure that satisfies certain conditions
• noun:   in World War II the alliance of Germany and Italy in 1936 which later included Japan and other nations

  Example: "The Axis opposed the Allies in World War II"

• noun:   the main stem or central part about which plant organs or plant parts such as branches are arranged
• noun:   a group of countries in special alliance