mid-15c., "non-animal life," originally any plant, from vegetable (adj.); specific sense of "plant cultivated for food, edible herb or root" is first recorded 1767. Meaning "person who leads a monotonous life" is recorded from 1921; sense of "one totally incapacitated mentally and physically" is from 1976.
The Old English word was wyrt (see wort). The commonest source of words for vegetables in Indo-European languages are derivatives of words for "green" or "growing" (compare Italian, Spanish verdura, Irish glasraidh, Danish grøntsager). For a different association, compare Greek lakhana, related to lakhaino "to dig."