(mathematics) The horizontal line in the complex plane, every point on which corresponds to a real number

On a steam locomotive, an axle connecting a coupled pair of unpowered wheels located in front of the driving wheels.

On a steam locomotive, an axle connecting a coupled pair of unpowered wheels located behind the driving wheels.

(biology) Containing only a single species of microorganism. For example, an "axenic culture" is a pure grown sample of the organism in question. / (biology) Isolated from organisms of any other species.

An axle which transfers power to a powered wheel from an engine, as in a steam locomotive.

(set theory) One of the axioms of set theory, equivalent to the statement that an arbitrary direct product of non-empty sets is non-empty; any version of said axiom, for example specifying the cardinality of the number of sets from which choices are made.

(geometry) Any of one or more lines about which a geometric figure is symmetric

The blade of an axe; or, a blade identical to that of an axe, but not actually part of one.

plural of axeblade

Dated spelling of axon.