Green’s Dictionary of Slang

1. an objector, a rebel, a dissenter, one who rejects the social status quo.

1788		Mass. Centinel 31 Dec. n.p.: Antis, and Fed, usurp the glory, So long enjoy’d by Whig and Tory [DA].
1830		Boston Transcript 31 Aug. 2/2: The masons, as the antis say, are clearly unfit for office — the Jacks are just as bad [DA].
1887		Dallas Dly Herald (TX) 28 Nov. 1/4: The antis carried every city precinct [...] and the antis are jubilant. Prohibitionists concede the victory.
1891		Opelousas Courier (LA) 29 Aug. 4/3: Now, white farmers and antis of the parish [...] do you want the nigger in yours?
1899		Wkly Messenger (St Martinsville, LA) 25 Nov. 2/2: The ring intended to capture the Fourth and Fifth ward, and defeat the antis in both.
1920		Wash. Herald (DC) 5 Sept. 14/5: Since I can’t use Slanguage in stories that I tell [...] I’ll leave the next line blank: (Come on, you antis! Do your duty!).

2. (Aus.) an anti-aircraft gun.

1932

(con. WWI) L. Mann Flesh in Armour 257: ‘The anties started going hell for leather’.