vegetative (adj.)

late 14c., "endowed with the power of growth," from Old French vegetatif "(naturally) growing," from Medieval Latin vegetativus, from vegetat-, past participle stem of vegetare (see vegetable (adj.)). Middle English transferred sense was "characterized by growth." Modern pathological sense of "brain-dead, lacking intellectual activity, mentally inert" is from 1893, via notion of having only such functions which perform involuntarily or unconsciously and thus are likened to the processes of vegetable growth.