Green’s Dictionary of Slang

1. a Turkish soldier.

1918		Kia Ora Coo-ee 15 Apr. 18/2: It was all over a damned clock, that he pinched from a Jacko, out at Beersheba. [Ibid.] 15 May 6/1: Tho’ they wished that every Turk had been a Hun; / For they rather like old ‘Jacko’, and they hate to give him pain, / But war is war – and battles must be won.
1921		N&Q 12 Ser. IX 424: Jacky. A Turk.
1924		(con. WWI) A.G. Pretty Gloss. of Sl. [...] in the A.I.F. 1921–1924 (rev. t/s) n.p.: Jacko. Nickname for the Turks used by the A.I.F. on Gallipoli and in Palestine.
1999		G. Seal Lingo 59: The enemy became johnny turk or jacko (also used in Australia for Aborigines, though once applied to the kookaburra, from one of its Lingo names the laughing jackass).

2. a kookaburra.

1922		Western Argus (Kalgoorlie, WA) 5 Dec. 35/2: Outback ‘jacky’ is regarded as the bushman’s clock, for at first streak of day this uncanny bird fills the paddock [...] with homeric peals of laughter.
1956		Argus (Melbourne) 16 Feb. 20/7: The Swaggie‘s Alarm Clock [...] We’ve called him ‘jacky’, ’laughing johnny’, ‘jacko’, breakfast bird’ and bushman’s cock’.
1941		Baker Popular Dict. Aus. Sl. 38: Jacko, a kookaburra.
1956		Argus (Melbourne) 16 Feb. 20/7: The Swaggie‘s Alarm Clock [...] We’ve called him ‘jacky’, ’laughing johnny’, ‘jacko’, breakfast bird’ and bushman’s cock’.
1999		see sense 1.