terrier vs bull terrier

terrier and bull terrier both are nouns.

Word	Noun	Adjective	Verb	Adverb
terrier	Yes	No	No	No
bull terrier	Yes	No	No	No

As nouns, bull terrier is a hyponym of terrier; that is, bull terrier is a word with a more specific, narrower meaning than terrier:

terrier: any of several usually small short-bodied breeds originally trained to hunt animals living underground
bull terrier: a powerful short-haired terrier originated in England by crossing the bulldog with terriers

terrier (noun)	bull terrier (noun)
any of several usually small short-bodied breeds originally trained to hunt animals living underground	a powerful short-haired terrier originated in England by crossing the bulldog with terriers