domestic dog vs barker

domestic dog and barker both are nouns.

Word	Noun	Adjective	Verb	Adverb
domestic dog	Yes	No	No	No
barker	Yes	No	No	No

As nouns, barker is a hyponym of domestic dog; that is, barker is a word with a more specific, narrower meaning than domestic dog:

domestic dog: a member of the genus Canis (probably descended from the common wolf) that has been domesticated by man since prehistoric times; occurs in many breeds
barker: informal terms for dogs

domestic dog (noun)	barker (noun)
a member of the genus Canis (probably descended from the common wolf) that has been domesticated by man since prehistoric times; occurs in many breeds	informal terms for dogs
	someone who stands in front of a show (as at a carnival) and gives a loud colorful sales talk to potential customers