semester hour vs credit hour

semester hour and credit hour both are nouns.

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

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

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

semester hour (noun)	credit 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