Authority on card games (5)
I believe the answer is:
hoyle
(Other definitions for hoyle that I've seen before include "Edmond --, early writer on card games" , "Sir Fred --, astronomer" , "English author, expert on card games, d.1769 - English astrophysicist, d. 2001" , "English astrophysicist, who coined the term "big bang", d. 2001" , "English astronomer who rejected the 'Big Bang' theory of the origins of the universe, d. 2001" .)