count vs countdown

count and countdown both are nouns.

Word	Noun	Adjective	Verb	Adverb
count	Yes	No	Yes	No
countdown	Yes	No	No	No

As nouns, countdown is a hyponym of count; that is, countdown is a word with a more specific, narrower meaning than count:

count: the act of counting; reciting numbers in ascending order
countdown: counting backward from an arbitrary number to indicate the time remaining before some event (such as launching a space vehicle)

Other hyponyms of count include blood count, census, nose count, nosecount, miscount, poll, recount, sperm count.

count (noun)	countdown (noun)
the act of counting; reciting numbers in ascending order	counting backward from an arbitrary number to indicate the time remaining before some event (such as launching a space vehicle)
a nobleman (in various countries) having rank equal to a British earl
the total number counted

count (verb)	countdown (verb)
include as if by counting
have faith or confidence in
take account of
determine the number or amount of
name or recite the numbers in ascending order
show consideration for; take into account
have weight; have import, carry weight
put into a group
have a certain value or carry a certain weight