bicycle vs safety bike

bicycle and safety bike both are nouns.

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

bicycle: a wheeled vehicle that has two wheels and is moved by foot pedals
safety bike: bicycle that has two wheels of equal size; pedals are connected to the rear wheel by a multiplying gear

Other hyponyms of bicycle include bicycle-built-for-two, tandem, tandem bicycle, mountain bike, off-roader, all-terrain bike, ordinary, ordinary bicycle, push-bike, safety bicycle, velocipede, pedelec, E-bike, electronic bicycle, electronic bike.

bicycle (noun)	safety bike (noun)
a wheeled vehicle that has two wheels and is moved by foot pedals	bicycle that has two wheels of equal size; pedals are connected to the rear wheel by a multiplying gear

bicycle (verb)	safety bike (verb)
ride a bicycle