Green’s Dictionary of Slang

zip v.²

to be quiet, to shut up.

1939		Howsley Argot: Dict. of Und. Sl. 55: zip – shut up.
1943		R.L. Bellem ‘Dead Man’s Shakedown’ in Dan Turner Detective Mar. 🌐 Suppose she kept her yap zippered about it until recently.
1983		J. Byrell (con. 1959) Up the Cross 103: They wanted the retaurateur to keep his gob zipped.
1996		J. Byrell Lairs, Urgers & Coat-Tuggers 295: [H]e gets told to zip his yap and just follow orders.
1999		K. Sampson Powder 53: He’d give it one last shot then zip up.
2008		A. Wheatle Dirty South 83: Davinia, zip your beak [...] and mind your business.
2009		T. Black Gutted 70: I said nowt. In the nick it’s policy: keep it zipped.
2010		Mail and Guardian (Johannesburg) 12 Feb. 🌐 We really want the president to zip up.
2013		T. Black Ringer [ebook] n.p.: I change tactics, try to keep it zipped. Seems the best policy in the circumstances.
2017		G. Gilmore Headland [ebook] ‘Anyone sniffing around your place looking for me, you zip it’.
2021		T. Pluck Boy from County Hell 91: ‘Zip it and follow me’.

In exclamations

zip it!

be quiet! shut up!

1983		C. Heath A-Team 2 (1984) 47: Zip it, Collins.
1996		J. Byrell Lairs, Urgers & Coat-Tuggers 171: ‘You didyer coin fair’n’square. So zip it!’.
1997		N. Barlay Curvy Lovebox 170: Zip it man.
2001		N. Barlay Hooky Gear 174: Zip it, I go, snatchin the 20 an stickin it back in his pocket.
2015		Valley Morn. Star (Harlingen, TX) 13 June 16/4: ‘Shut your ass up [...] zip it!’.