a long, narrow, thin strip of wood, metal, etc.; slat.

a long, flexible strip of wood or the like, used in drawing curves.

Machinery .

any of a series of uniformly spaced ridges on a shaft, parallel to its axis and fitting inside corresponding grooves in the hub of a gear, etc., to transmit torque.

feather key.

Building Trades . a thin strip of material inserted into the edges of two boards, acoustic tiles, etc., to make a butt joint between them; a feather.

Mathematics, Engineering . a function that has specified values at a finite number of points and consists of segments of polynomial functions joined smoothly at these points, enabling it to be used for approximation and interpolation of functions.

to provide with a spline or key.

to provide with a keyway.