first moment vs arithmetic mean

first moment and arithmetic mean both are nouns.

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

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

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

Other synonyms of first moment include expectation, expected value.

first moment (noun)	arithmetic mean (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