Green’s Dictionary of Slang

(Aus.) a piano.

1918		7th Field Artillery Brigade Yandoo Jan. 97: Did you know the 7th has a Y.M.C.A. now? Rather! We have got a ‘gohanna’ too [AND].
1921		(con. WWI) E. Lynch Somme Mud 327: ‘Lend a hand to move this piano’ [...] Longun rushes out and tells the sergeant-major to ‘send four men in to shift the flamin’ goanna.’.
1931		Queenslander (Brisbane) 25 June 39/1: Some [boy scout] packs are fortunate enough to have a piano [...] Cubs from the South Side gathered round the old ‘goanna’.
1939		Advocate (Burnie, Tas.) 15 May 11/2: Gortio Goanna will play the piano.
1945		Baker Aus. Lang.
1965		F.J. Hardy Yarns of Billy Borker 39: A fella named Light Fingers Jackson from Woolloomooloo stole the Steinway grand piano. He went out in a boat with his mate in the middle of the night, grabbed the grand goanna.
1967		‘Whisper All Aussie Dict.’ in Kings Cross Whisper (Sydney) xxxv 6/1: goanna: [sic] Piano.
1978		Aus. Women’s Wkly 15 Mar. 80/1: I learned the goanna for a year.
1999		G. Seal Lingo 91: A goanna is rhyming slang on rhyming slang for joanna, meaning piano.