credit hour vs semester hour

credit hour and semester hour both are nouns.

Word	Noun	Adjective	Verb	Adverb
credit hour	Yes	No	No	No
semester hour	Yes	No	No	No

As nouns, credit hour and semester hour are synonyms defined as:

credit hour and semester hour: a unit of academic credit; one hour a week for an academic semester

credit hour (noun)	semester hour (noun)
a unit of academic credit; one hour a week for an academic semester	a unit of academic credit; one hour a week for an academic semester