It's the British version of shut up.
Could also mean 'fasten your seatbelt'.
1. She told the students to belt up because they were making so much noise.
2. I told the kids to BELT UP before I started the car.
31π 7π
Going to shoot up (ice etc), particularly tightening a belt around forearm to highlight veins (as nurses do)
"Ay der Marko bruva, we going to belt up or what cuz?!"
1π 4π
british slang for shut up, a rude way to tell someone to be quiet.
6π 1π
Australian version of "stick/shove/ram/cram/jam/poke it up your arse"
Belt it up your arse: "When the mechanic told me it was gonna cost five hundred bucks to fix me car, I told him to belt it up his arse."
19π 11π
When a person is about to fight and they want someone to hold them back. Itβs basically saying hold me back like a belt holds up pants, or a seat belt holds up back.
Yo girl you need to belt me up now!