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Wiktionary
count down

n. (alternative spelling of countdown English) vb. 1 To announce the passage of time to a precisely timed expected event. 2 To await a precisely timed expected event.

WordNet
count down

v. count backwards; before detonating a bomb, for example

Usage examples of "count down".

Now he stands in a lobby of the Foote Mansion, watching electric numbers above an elevator count down, occasionally sneaking a glance at himself in a big mirror.