The first known use of the word leonine in literature was in the 12th-century romance Guillaume d'Angleterre. The word leonine is an adjective that means "like a lion" or "resembling a lion". 

According to the Oxford English Dictionary, the first known use of "leonine" in English was around the late 14th century, appearing in the writings of Geoffrey Chaucer, the renowned poet of that period; essentially meaning it was used during the Middle English era. 

There were 13 Popes that used the name Leo, and as far as I can tell, that was not their name before they became Pope.  The first was Leo I (440-461), also referred to as Leo the Great (only 3 Popes were ever given the title of Great), and the last was Leo XIII (1878-1903).  I wonder if they took the name Leo because they viewed themselves as Leonine?  

1 hour ago, drpaladin said:

Leo the Great was named Leo from birth.

Popes used their own first names until John II in 533.

Sorry, I missed that, but did you know that he was succeeded by Pope Hilarius.  I wonder if he was also hilarious? 

On GA we have three authors who are "Leo". I wonder how many members are a "Leo"?

28 minutes ago, Paladin said:

On GA we have three authors who are "Leo". I wonder how many members are a "Leo"?

Do you mean the authors' names are Leo or that is their Zodiac sign? 

20 minutes ago, Bill W said:

Do you mean the authors' names are Leo or that is their Zodiac sign? 

Names are Leo. I've no idea how to work out their Zodiac sign. Of course using the Chinese Zodiac the equivalent would be Tiger.