birdbrain vs loon

birdbrain and loon both are nouns.

Word	Noun	Adjective	Verb	Adverb
birdbrain	Yes	No	No	No
loon	Yes	No	No	No

As nouns, birdbrain and loon are synonyms defined as:

birdbrain and loon: a person with confused ideas; incapable of serious thought

Other synonyms of birdbrain include addle-head, addlehead.

birdbrain (noun)	loon (noun)
a person with confused ideas; incapable of serious thought	large somewhat primitive fish-eating diving bird of the Northern Hemisphere having webbed feet placed far back; related to the grebes
	a worthless lazy fellow
	a person with confused ideas; incapable of serious thought