kilometers per second vs km/s

kilometers per second and km/s both are nouns.

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

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

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

Other synonyms of kilometers per second include kilometres per second.

kilometers per second (noun)	km/s (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).