decametre vs decameter

decametre and decameter both are nouns.

Word	Noun	Adjective	Verb	Adverb
decametre	Yes	No	No	No
decameter	Yes	No	No	No

As nouns, decametre and decameter are synonyms defined as:

Other synonyms of decametre include dam, dekameter, dekametre, dkm.

decametre (noun)	decameter (noun)
a metric unit of length equal to ten meters	a metric unit of length equal to ten meters