ruminant |ˈro͞omənənt| noun1 an even-toed ungulate mammal that chewsthe cud regurgitated from its rumen. Theruminantscomprisethe cattle, sheep, antelopes, deer, giraffes, and their relatives. 2 a contemplative person; a person given to meditation.adjectiveof or belonging to ruminants.ORIGIN mid 17th cent.: from Latin ruminant- ‘chewing over again,’from the verb ruminari, from rumen ‘throat’ (see rumen) .
So if someone says "You're such a ruminant!" they're either calling you a sheep or a deep thinker. Perhaps all sheep are deep thinkers.