Green’s Dictionary of Slang

September morn n.

[rhy. sl. = horn n.2 (1d); note September Morn, a painting by Paul Chabas of a young woman bathing nude, which was first exhibited at the 1912 Salon in Paris. Censors attempted to ban a reproduction of the picture from public exhibition in the US, a farcical effort, which led to the sale of more than seven million reproductions – appearing on dolls, statues, umbrella handles, tattoos and many other places – and the assurance that Chabas need never work again]

an erection.

[UK]R. Puxley Fresh Rabbit.