Green’s Dictionary of Slang

(US campus) cigarette.

1967–8		Baker et al. CUSS 184: Rette Cigarette.
1971		Current Sl. VI 9: Ret, n. A cigarette.
2003		(con. 1971) J. Hudgins in Midnight Sun Online newsletter for Robert E. Peary High School Alumni VIII:1 🌐 Memorable Incident: The first week of school ‘the crew’ went to bathroom where I was smoking a ret and put a cherry boom in the toilet.