earned run average vs ERA

earned run average and ERA both are nouns.

Word	Noun	Adjective	Verb	Adverb
earned run average	Yes	No	No	No
ERA	Yes	No	No	No

As nouns, earned run average and ERA are synonyms defined as:

earned run average and ERA: (baseball) a measure of a pitcher's effectiveness; calculated as the average number of earned runs allowed by the pitcher for every nine innings pitched

earned run average (noun)	ERA (noun)
(baseball) a measure of a pitcher's effectiveness; calculated as the average number of earned runs allowed by the pitcher for every nine innings pitched	(baseball) a measure of a pitcher's effectiveness; calculated as the average number of earned runs allowed by the pitcher for every nine innings pitched