E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Geryon (g hard).
A human monster with three bodies and three heads, whose oxen ate human flesh, and were guarded by a two-headed dog. Herculs slew both Geryon and the dog. This fable means simply that Geryon reigned over three kingdoms, and was defended by an ally, who was at the head of two tribes.