A flight feather that appears between the primaries and secondaries on some birds.

A plane parallel to the surface of a tooth.

Relating to, resembling, or situated on an axis

Belonging to the axis of the body, or to the axis of any appendage or organ

"the axial bones"

In the same direction as the axis, parallel to the axis.

"The secondary xylem usually consists of axial and radial elements."