A leopard is literally a "lion-panther". In ancient times, the animal was thought to be a hybrid of the species, a middle ground, and so the people back then named it thus. As we move backwards, in Middle English, it underwent alterations such as lubard, lybard, libbard, and lebard (these variations we've seen so much are due to decentralization and lack of standards back then), from a similar myriad of Old French phonemic jumbles. Ironically, the Latin root, lepardus, is closer to the modern word than most of the changes. That in turn is from Ancient Greek lepardos, and since they were the ones who named the animal, they got to combine their words leon, "lion", and pardos, "panther". Both words are unknown in origin, with leon possibly not even having IE roots, and pardos potentially having a cognate in Sanskrit pradukh, meaning "tiger". Lions and tigers and leopards, oh my!
Adam Aleksic, a rising sophomore studying linguistics and government at Harvard University, has been described as the internet's sixth most famous etymologist. He also has disturbing interests in politics, vexillology, geography, board games, conlanging, and law.