bike vs motorbike

bike and motorbike both are nouns.

Word	Noun	Adjective	Verb	Adverb
bike	Yes	No	Yes	No
motorbike	Yes	No	Yes	No

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

bike: a motor vehicle with two wheels and a strong frame
motorbike: small motorcycle with a low frame and small wheels and elevated handlebars

Other hyponyms of bike include minibike, dirt bike, scrambler, trail bike.

bike (noun)	motorbike (noun)
a wheeled vehicle that has two wheels and is moved by foot pedals	small motorcycle with a low frame and small wheels and elevated handlebars
a motor vehicle with two wheels and a strong frame

bike (verb)	motorbike (verb)
ride a bicycle	ride a motorcycle