arithmetic mean vs first moment

arithmetic mean and first moment both are nouns.

Word	Noun	Adjective	Verb	Adverb
arithmetic mean	Yes	No	No	No
first moment	Yes	No	No	No

As nouns, arithmetic mean and first moment are synonyms defined as:

arithmetic mean and first moment: the sum of the values of a random variable divided by the number of values

Other synonyms of arithmetic mean include expectation, expected value.

arithmetic mean (noun)	first moment (noun)
the sum of the values of a random variable divided by the number of values	the sum of the values of a random variable divided by the number of values