ˈ ̷ ̷| ̷ ̷ noun
( -s )
Etymology: count down, v.
: an audible backward counting off in fixed units (as seconds) from an arbitrary starting number (as 10) to mark the diminishing time remaining before the execution of an operation
the countdown concluded, “four, three, two, one,” and then the firing button was pushed
also : the length of time marked by such a counting or required by the entire sequence of steps in readying a missile for flight — compare zero hour