kilometer vs kilometre

kilometer and kilometre both are nouns.

Word	Noun	Adjective	Verb	Adverb
kilometer	Yes	No	No	No
kilometre	Yes	No	No	No

As nouns, kilometer and kilometre are synonyms defined as:

kilometer and kilometre: a metric unit of length equal to 1000 meters (or 0.621371 miles)

Other synonyms of kilometer include klick, km.

kilometer (noun)	kilometre (noun)
a metric unit of length equal to 1000 meters (or 0.621371 miles)	a metric unit of length equal to 1000 meters (or 0.621371 miles)