Green’s Dictionary of Slang

1. (US, also seggie) a segregationist.

1970		New Yorker 12 Dec. 107: Fulbright for the first time openly appealed for black votes, because he believed that he couldn’t win without them and that the ‘seggies’ [...] would vote against him.
1971		Harper’s Mag. Jan. 35: When people wore the American flag then it was to show that they were not segs, because the segs of course wore the Confederate flag.

2. (prison) a segregation unit or cell.

1967		M. Braly On the Yard (2002) 202: I’m full up to here with that white-faced punk [...] If it were up to me, I’d throw him in seg and throw away the key.
1971		F. Hilaire Thanatos 89: Play it right and we’ll all be out of seg in six months.
1978		R. Caron Go-Boy! 269: He was in ‘seg’ for shanking another con.
1986		J. Campbell Gate Fever 99: Mr Carrol gave me a quick summary of the routine for a prisoner being held ‘in seg’.
1995		J. Cameron Vinnie Got Blown Away 24: So he lost his time like he wanted and a couple days down the seg.
2004		Guardian G2 4 Mar. 18: Sid had been shipped out of a high-security jail and because of lack of space in the seg unit, straight into the hospital wing of another.
2011		J.J. Connolly Viva La Madness 78: [The] added buried-deep-then-dug-up concrete complexion — the Seg Block suntan.
2016		Mother Jones July/Aug. 🌐 I ask one of the regular white-shirted COs what an average day in seg looks like.

3. (N.Z. prison) an inmate who is on segregation.

2001

D. Looser Boobslang [U. Canterbury D.Phil. thesis] 161/1: seggie n. an inmate on segregation.