The hircocervus (, "billy goat" + cervus, "stag") or tragelaph (, "billy goat" + έλαφος, elaphos, "stag"), also known as a goat-stag or horse-stag, was a legendary creature imagined to be half-goat, half-stag. In his work De Interpretatione, Aristotle utilized the idea of a fabulous goat-stag to express the philosophical concept of something that is knowable even though it does not really exist. In Plato's Republic, Socrates speaks of his own image-making as similar to that of painters who paint goat-stags, combining the features of different things together (488a).