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1.
n.

1) an unreliable New York City subway line that is the underground transportation equivalent of the BQE (Brooklyn-Queens Expressway), as it does not enter Manhattan at all.

2) also known as the GG (or double G) in the 80's because if you rode this line, you were as good as gone.

3) connects to the L-train at the Metropolitan (G)/Lorimer (L) stop.
I had to wait 35 minutes for the G-train this morning. Needless to say, I was late for work...AGAIN!
by kstar November 13, 2004
 
2.
Annoying, unreliable and/or weak and a waste of time - similar to the G train line in Brooklyn. Can be shortened to just "G" or "G-shit" or replaced by cupping the fist into a G-shape.
You going to Bob's party? Nah, that's G-train.
by Jobu October 14, 2006
 
3.
Also referred to as the "ghost train", a near mythical subterranean dweller of New York City.

Unconfirmed reports of its existence lie from the uterus of Queens to the ballsac of Brooklyn.

Slang: Fucking G train
"Where is the fucking G Train...??"

"This is Lorimer Street Station. Transfer downstairs to the Fucking G. Stand clear of the closing doors."
by the 'hof May 15, 2010
 
4.
A male who accumulates many female G-string underwear.
That dude is a G-train! you saw him at that party?
by ImaGtrain October 15, 2011
 
5.
1. a student band at deerfield academy
2. ms. Gladding, who the band was name after
1. "did you hear? g-train is opening for the grift on friday night"
2. "looks its the g-train!"
by bri-izzle January 18, 2007