atheneum, n. — Green’s Dictionary of Slang

atheneum n.

[? the Athenaeum Club, London, which might be seen as the fount of all wisdom]

the penis.

1890–1904		Farmer & Henley Sl. and Its Analogues.
c.1904		A. Crowley Snowdrops from a Curate’s Garden 25: Charles’ Athenaeum was held firmly in the palm of his hand by his thumb.