mileage vs travel reimbursement

mileage and travel reimbursement both are nouns.

Word	Noun	Adjective	Verb	Adverb
mileage	Yes	No	No	No
travel reimbursement	Yes	No	No	No

As nouns, travel reimbursement is a hypernym of mileage; that is, travel reimbursement is a word with a broader meaning than mileage:

Other hypernyms of mileage include travel allowance.

mileage (noun)	travel reimbursement (noun)
distance measured in miles	a sum allowed for travel
a travel allowance at a given rate per mile traveled
the ratio of the number of miles traveled to the number of gallons of gasoline burned