“Leonine” comes from the Latin “leo,” meaning “lion,” and while we’re using “leonine” as an adjective referencing lions or anything resembling a lion, it can also be used as a capital “L” adjective. In that sense, “Leonine” means “relating to one of the popes named Leo, especially Leo IV and the part of Rome that he fortified.” The capital “L” version can also refer to a style of medieval poetry written in hexameter. It’s attributed to a medieval poet named Leo, but details of his identity and any identifiable works have been lost to history.