easy money vs gravy train

easy money and gravy train both are nouns.

Word	Noun	Adjective	Verb	Adverb
easy money	Yes	No	No	No
gravy train	Yes	No	No	No

As nouns, easy money and gravy train are synonyms defined as:

easy money (noun)	gravy train (noun)
income obtained with a minimum of effort	income obtained with a minimum of effort
the economic condition in which credit is easy to secure