all-terrain bike vs off-roader

all-terrain bike and off-roader both are nouns.

Word	Noun	Adjective	Verb	Adverb
all-terrain bike	Yes	No	No	No
off-roader	Yes	No	No	No

As nouns, all-terrain bike and off-roader are synonyms defined as:

all-terrain bike and off-roader: a bicycle with a sturdy frame and fat tires; originally designed for riding in mountainous country

Other synonyms of all-terrain bike include mountain bike.

all-terrain bike (noun)	off-roader (noun)
a bicycle with a sturdy frame and fat tires; originally designed for riding in mountainous country	a bicycle with a sturdy frame and fat tires; originally designed for riding in mountainous country