tonne-kilometre vs tonne-kilometer

tonne-kilometre and tonne-kilometer both are nouns.

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

As nouns, tonne-kilometre and tonne-kilometer are synonyms defined as:

tonne-kilometre and tonne-kilometer: a unit of measure used in freight transport which determines the transport of one tonne of goods by a transport mode over one kilometer.

Other synonyms of tonne-kilometre include tkm.

tonne-kilometre (noun)	tonne-kilometer (noun)
a unit of measure used in freight transport which determines the transport of one tonne of goods by a transport mode over one kilometer.	a unit of measure used in freight transport which determines the transport of one tonne of goods by a transport mode over one kilometer.