directrix

As a noun directrix

is a female who directs; a directress.

As an adjective undefined is

lacking a definition or value.

As nouns the difference between director and directrix

is that director is one who directs; the person in charge of managing a department or directorate (eg, director of engineering''), project, or production (as in a show or film, eg, ''film director ) while directrix is a female who directs; a directress.

In geometry terms the difference between generatrix and directrix

is that generatrix is a curve that, when rotated about an axis, produces a solid figure while directrix is a line used to define a curve or surface; especially a line, the distance from which a point on a conic has a constant ratio to that from the focus.