Green’s Dictionary of Slang

(Aus.) one who lived deep in the mountains adjacent to Adelaide, SA; often an escaped convict from NSW or Van Dieman’s land (Tasmania) on the run.

1845		S. Aus. Gaz. 22 Nov. 2/5: William Maitland, a tiersman, was again brought up on the charge of stealing and slaughtering a bullock the property of some person unknown.
1849		S. Aus. Register (Adelaide) 20 Oct. 3/4: Thomas Adams, a Tiersman, charged with being drunk in Rundle-srreet, pleaded guilty, and was fined 5s.
1855		S. Aus. Register (Adelaide) 12 Apr. 3/5: A young woman living with a Tiersman in the Mount Lofty Range, named Holland, had died suddenly on the previous evening under suspicious circumstances.
1941		Baker Popular Dict. Aus. Sl. 76: ‘Tiersman’: one who lives in the mountains. Tasmanian slang.