vegetable + -arian; popularized following 1847 foundation of British Vegetarian Society. (Alternatively, it may derive from vegetus + -arian.)
(animal that eats only plants): herbivore (standard term)
vegetarian (plural vegetarians) A person who does not eat animal flesh, or, in some cases, animal products. 1897, Robert Hunter and Charles Morris, Universal Dictionary of the English Language, volume 4, page 5045: Vegetarian Society A society formed at Manchester in 1847, to promote the use of cereals, pulse, and fruit, as articles of diet; and to induce habits of abstinence from fish, flesh, and fowl, as food. 1897, Robert Hunter and Charles Morris, Universal Dictionary of the English Language, volume 4, page 5045: vegetarian One who abstains from animal food, living exclusively on vegetables, milk, eggs, and the like. The more strict vegetarians eat vegetables and farinaceous food only, abstaining from eggs, butter, milk, and in some cases, honey. An animal that eats only plants; a herbivore.
Adjective vegetarian (comparative more vegetarian, superlative most vegetarian) Of or relating to the type of diet eaten by vegetarians (in all senses). Of a product normally made with meat, having non-meat substitutes in place of meat. 2008, Wil Forbis, Acid Logic: A Decade of Humorous Writing on Pop Culture, Trash Cinema, and Rebel Music, p. 208: Is there such a thing as a good tasting vegetarian hot dog? Cuz every one I've tried tasted like smelted tire. (of a person) That does not eat meat. I have a vegetarian brother
(animal that also eats meat): omnivore (animal that only eats meat): carnivore (person that only eats meat): meatarian, meatatarian