The Collaborative International Dictionary
Graminivorous \Gram"i*niv"o*rous\, a. [L. gramen, graminis, grass + vorare to eat greedily.] Feeding or subsisting on grass, and the like food; -- said of horses, cattle, and other animals.
Douglas Harper's Etymology Dictionary
"feeding on grass," 1739, from gramini-, comb. form of Latin gramen (genitive graminis) "grass, fodder," which perhaps ultimately is cognate with English grass, + -vorous.
Wiktionary
a. (context entomology English) That eats grasses and seeds.
Usage examples of "graminivorous".
No little Gradgrind had ever associated a cow in a field with that famous cow with the crumpled horn who tossed the dog who worried the cat who killed the rat who ate the malt, or with that yet more famous cow who swallowed Tom Thumb: it had never heard of those celebrities, and had only been introduced to a cow as a graminivorous ruminating quadruped with several stomachs.
I even entertained some idea of putting myself on a vegetable diet, vaguely conceiving that, in becoming a graminivorous animal, I should sacrifice to Dora.