Green’s Dictionary of Slang

1. the anus [arsehole n. (1) (pron. ‘arssle’)].

1969		S.T. Kendall Up the Frog.
1977		D. Powis Signs of Crime 182: Elephant (& Castle) Anus.
1989		J. Morton Lowspeak.
1992		R. Puxley Cockney Rabbit.
1991		Age (Melbourne) 7 Dec. 130/7: ‘You’re an Elephant and Castle’.
2003		B. Dark Dirty Cockney Rhy. Sl.

2. a parcel.

1959

J. Gosling Ghost Squad 24: Thieves’ argot, spoken properly, is a foreign language which needs to be learned [...] Among the words and phrases derived from rhyming slang are: [...] ‘Elephant’ equals ‘Elephant and Castle’ (pronounced ‘Carsel’) which means a parcel.