COUNTDOWN
countdown
(noun) counting backward from an arbitrary number to indicate the time remaining before some event (such as launching a space vehicle)
Source: WordNet® 3.1
Etymology
Noun
countdown (plural countdowns)
A count backward in fixed units to the time of some event, especially the launch of a space vehicle.
The acts of preparation carried out during this period.
A radio or television program counting down the top songs of a given week, usually in reverse order ending with the No. 1.
Verb
countdown (third-person singular simple present countdowns, present participle countdowning, simple past and past participle countdowned)
(nonstandard) To count down.
Source: Wiktionary