merl vs blackbird

merl and blackbird both are nouns.

Word	Noun	Adjective	Verb	Adverb
merl	Yes	No	No	No
blackbird	Yes	No	No	No

As nouns, merl and blackbird are synonyms defined as:

Other synonyms of merl include European blackbird, merle, ousel, ouzel, Turdus merula.

merl (noun)	blackbird (noun)
common black European thrush	any bird of the family Icteridae whose male is black or predominantly black
	common black European thrush