freightage vs charge per unit

freightage and charge per unit both are nouns.

Word	Noun	Adjective	Verb	Adverb
freightage	Yes	No	No	No
charge per unit	Yes	No	No	No

As nouns, charge per unit is a hypernym of freightage; that is, charge per unit is a word with a broader meaning than freightage:

Other hypernyms of freightage include rate.

freightage (noun)	charge per unit (noun)
transporting goods commercially at rates cheaper than express rates	amount of a charge or payment relative to some basis
the charge for transporting something by common carrier