Definition of "rheostatic"

Rheostatic braking is achieved by excitation of the traction motor fields from a separate step-down transformer, fed from the main transformer under control of the main tap changer. The output of this transformer is fed through the normal power rectifiers. Rheostatic braking is thus controlled by the main control handle after movement of a selector switch to braking instead of power.

1960 December, “The first hundred 25 kV a.c. electric locomotives for B.R.”, in Trains Illustrated, pages 728–729