km/s vs kilometers per second

km/s and kilometers per second both are nouns.

Word	Noun	Adjective	Verb	Adverb
km/s	Yes	No	No	No
kilometers per second	Yes	No	No	No

As nouns, km/s and kilometers per second are synonyms defined as:

km/s and kilometers per second: the ratio of the distance traveled (in kilometers) to the time spent traveling (in seconds).

Other synonyms of km/s include kilometres per second.

km/s (noun)	kilometers per second (noun)
the ratio of the distance traveled (in kilometers) to the time spent traveling (in seconds).	the ratio of the distance traveled (in kilometers) to the time spent traveling (in seconds).