first cause vs primum mobile

first cause and primum mobile both are nouns.

Word	Noun	Adjective	Verb	Adverb
first cause	Yes	No	No	No
primum mobile	Yes	No	No	No

As nouns, first cause and primum mobile are synonyms defined as:

first cause and primum mobile: an agent that is the cause of all things but does not itself have a cause

Other synonyms of first cause include prime mover.

first cause (noun)	primum mobile (noun)
an agent that is the cause of all things but does not itself have a cause	an agent that is the cause of all things but does not itself have a cause