double birdie vs eagle

double birdie is not a noun while eagle is a noun.

Word	Noun	Adjective	Verb	Adverb
double birdie	No	No	Yes	No
eagle	Yes	No	Yes	No

As verbs, double birdie and eagle are synonyms defined as:

double birdie (noun)	eagle (noun)
	any of various large keen-sighted diurnal birds of prey noted for their broad wings and strong soaring flight
	an emblem representing power
	a former gold coin in the United States worth 10 dollars
	(golf) a score of two strokes under par on a hole

double birdie (verb)	eagle (verb)
shoot two strokes under par	shoot in two strokes under par
	shoot two strokes under par