Green’s Dictionary of Slang

1. (Aus.) an Aboriginal; the predecessor of the modern abo n. (1)

1999

G. Seal Lingo 10: Far more derogatory expressions persist in Lingo, including nigger, boong, abo (now often shortened to ab), coon and gin.

2. (US) an Abolitionist.

1862		Elias R. Boles letter 28 Feb. The Abs came toward us and we showed fight to them and they backed off. [...] Good gracious the Abs does run.
1862		Peticolas diary 21 Feb. in Alberts (ed.) Rebels on the Rio Grande 1984 43: The Ab’s had gotten in 30 yards of us, and I began to load and shoot as fast as I could. [Ibid.] 22 Feb. 49: We took supper last night on provisions abandoned by the Abs in their flight.
1908		(con. 1862) G.H. Pettis The California Column [online] The rebels, before they left, had publicly announced that the ‘Abs’ (abolitionists ?) would soon take the fair city, which would then be given over to the ravages of a brutal soldiery.
2006		(ref. to 1861) Jay W. Sharp A Soldier of the Trails at www.desertusa.co 🌐 On October 1, 1861, only some three months after his 17th birthday, Thomas Edwin Jackson, fired by patriotism, enlisted as a private [...] In his heart, he probably yearned to fight the Abolitionists, or ‘Abs,’ in glorious battles in the east.

3. an abdominal muscle, usu. in the context of a flat stomach; often in pl.

1967		J. Rechy Numbers (1968) 66: The relative merits of ‘frog kicks’ for the ‘abs’ as opposed to regular situps.
1994		G. Indiana Rent Boy 38: At the gym, pumping lats and abs and pecs.
1998		R.G. Barrett Mud Crab Boogie (2013) [ebook] Billy suggested they [...] paddle four laps of Bondi, do a few rounds on the heavy bag, then finish with some ab-work.
1999		Indep. Real Life 25 July 3: Being slim with small boobs, flat abs.
2002		J. Franzen Corrections 95: He repositioned it against his abs and tucked in the sweater.
2005		L. Redhead Rubdown [ebook] Spent the rest of the time lifting free weights and working on my abs.
2011		Sydney Morning Herald 27 Dec. 🌐 Everyone wants great skin and flat abs.
2010		L. Berney Gutshot Straight [ebook] Good abs, she suspected.
2013		F. Bill Donnybrook [ebook] The muscles of his abs and legs rang tight.
2016		A. Wheatle Crongton Knights 227: ‘Queen Belly Blender can stir up her abs like a roundabout full of hot-wheeling cabs!’.

4. attrib. use of sense 3.

2007

C. Goffard Snitch Jacket 165: What you need is some ab work [...] some military presses, quads, lats, and glutes.

5. (Aus.) abalone.

2002

S. Maloney Something Fishy (2006) 33: Some desperado with several grand of illegal ab in one hand and a diving knife in the other.