Green’s Dictionary of Slang

1. (US, also ag coll) an agricultural college.

[1895		Capitol Jrnl (Salem, OR) 7 June 1 Mile Bicycle Race [...] A.S. Wood, Ag. Coll: .
1942		Berrey & Van den Bark ATS: §829/2: Ag, ag coll, aggie, cow college, an agricultural college .
1992		(con. 1920s) F.M. Davis Livin’ the Blues 73: Rival schools sneeringly termed it a ‘cow college’ and headline writers abbreviated it to K-Aggies.

2. an agricultural student.

1913		Daily Nebraskan 20 Feb. in DN IV:ii 144: [Headline] Aggies Can Not Break Up Magnificent Machine Work of Stiehm’s Men.
1914		E. Wittmann ‘Clipped Words’ in DN IV:ii 133: ag, from agricultural student. [...] ‘The ags had a good stunt on University night.’.
1925		S. Lewis Arrowsmith 28: Indignant meetings to denounce the proposal to let the ‘aggies’ use the North Side Tennis Courts.
1968		G. Slatter Pagan Game (1969) 110: Always sending for a chit from the Head every time he had to [...] instruct the Ag boys on farm management.
1972		D. Jenkins Semi-Tough 170: There were scrawny old Aggies whose daddies had made them go there in the first place, to Texas A&M.

3. a country bumpkin.

1942

Berrey & Van den Bark Amer. Thes. Sl. §391.3: Rustic; Bumpkin, ag, aggie, aggy.

4. agriculture; also as adj.

1963		R. McGregor-Hastie Compleat Migrant 8: Not Sir Wonderway Aygot-Thissere job of the Min. of Ag.
1976		R. Hall Glide Time 93: boss: It’s promotion. beryl: To Ag and Fish.
2001		‘John le Carré’ Constant Gardener 340: On secondment from the Min of Ag and Fish.
2005		P. Temple Broken Shore (2007) [ebook] Every second dickhead wants to live in the county [...] fuckin up the roads, moanin about the cowshit and the ag chemicals.