Millenary is the adjective form of millennium (1000 years) and millenarian (a word similar to octogenarian). A mossback refers to a very old turtle or shellfish which has algae growing on its back. Mossback is also a word used to refer to a very old-fashioned or conservative person. So, a Millennary Mossback would be a 1000-year old turtle that has moss growing on its back (though, technically every model is a mossback since they all have moss growing on their shells). Eastern folklore also states when a tortoise becomes 1000 years old, it learns the ability to speak human languages and prophesize the future.