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1. keep six
To hang back and watch out for somebody when they are going into a potentially dangerous situation. As in before a large illegal transaction, or while conducting a robbery.

Has nothing to do with police being 5-0. Actually derived from military communications. When an infantry squad is moving, one member may be assigned to "watch the squad's 6", meaning their 6 o'clock (behind them).
Alright guys, there's supposed to be no guns inside the pool hall, so you stay out here and keep six for me. If I you hear shots or I'm not out in 20 minutes, come in blasting.
2. KEEP SIX
to watch over; be a lookout for
"stay by the window and keep six for any cops."
by bmoc Nov 6, 2003 add a video
3. Keep Six
to be on the lookout
For example a robbery is being committed and one robber tells the other to go outside and KEEP SIX
4. KEEP SIX
To keep a look out for police, derived from cops being 5.0, so six means you're one up on the cops.
I'll park here and roll this up if you keep six!
by vijay Dec 3, 2003 add a video
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