speed of light vs velocity

speed of light and velocity both are nouns.

Word	Noun	Adjective	Verb	Adverb
speed of light	Yes	No	No	No
velocity	Yes	No	No	No

As nouns, velocity is a hypernym of speed of light; that is, velocity is a word with a broader meaning than speed of light:

speed of light: the speed at which light travels in a vacuum; the constancy and universality of the speed of light is recognized by defining it to be exactly 299,792,458 meters per second
velocity: distance travelled per unit time

Other hypernyms of speed of light include constant, speed.

speed of light (noun)	velocity (noun)
the speed at which light travels in a vacuum; the constancy and universality of the speed of light is recognized by defining it to be exactly 299,792,458 meters per second	distance travelled per unit time