zero hour
the time when something has to be decided or done (there can be no more waiting)

– examples

“Well everyone, after 3 weeks of debate, this is zero hour. It is now, or never


zero tolerance
no lenience; no breaking of the law will be allowed

– examples

Recently the government announced it would introduce a new zero tolerance law on drugs


zip it
(spoken)
be quiet; shut up

– examples

“You know you should have let me do it. I know far more about this stuff than you.”
“Oh, zip it. I don’t need your advice.”


Z Day
(taken from ‘D-Day’, the day in World War 2 when the allies counter-attacked the German forces by landing in France)
an imagined day when mankind must fight zombies to the death

– examples

I don’t know about you, but I want to know how to fire a gun in case z-day finally arrives.

Anne is an incredible athlete. I would want her on my team when z-day arrives