expectation vs first moment

expectation and first moment both are nouns.

Word	Noun	Adjective	Verb	Adverb
expectation	Yes	No	No	No
first moment	Yes	No	No	No

As nouns, expectation and first moment are synonyms defined as:

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

Other synonyms of expectation include arithmetic mean, expected value.

expectation (noun)	first moment (noun)
belief about (or mental picture of) the future	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
the feeling that something is about to happen
anticipating with confidence of fulfillment