Green’s Dictionary of Slang

death by hanging.

1860		Hotten Dict. of Modern Sl. etc. (2nd edn) 91: Autumn a slang term for an execution by hanging. When the drop was introduced instead of the old gallows, cart, and ladder, and a man was for the first time ‘turned-off’ in the present fashion, the mob were so pleased with the invention that they spoke of the operation as at autumn, or the fall of the leaf.
1874		Pembs. Herald (Wales) 8 May 4/3: Puns produce odd new terms, as when the old hangman's machinery of cart and ladder was superseded by the ‘drop,’ and the appreciating crowd spoke of its being ‘autumn’ with the criminal, meaning the ‘fall of the leaf’.