belt up
phrasal verb with belt verb uk/belt/ us/belt/
UK
(BE QUIET)
very informal住嘴，安静下来
used to tell someone to stop talking or making a noise
Just belt up, will you! I'm trying to concentrate. 你闭嘴！我正在想问题。
(FASTEN)
informal (US buckle up)系紧安全带
to fasten the belt that keeps you in your seat in a car or a plane
Don't forget, belt up before you drive off. 别忘了开车前系好安全带。