ratter vs rat terrier

ratter and rat terrier both are nouns.

Word	Noun	Adjective	Verb	Adverb
ratter	Yes	No	No	No
rat terrier	Yes	No	No	No

As nouns, ratter and rat terrier are synonyms defined as:

ratter and rat terrier: any of several breeds of terrier developed to catch rats

ratter (noun)	rat terrier (noun)
any of several breeds of terrier developed to catch rats	any of several breeds of terrier developed to catch rats
a disloyal person who betrays or deserts his cause or religion or political party or friend etc.