light speed vs velocity

light speed and velocity both are nouns.

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

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

light speed: 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 light speed include constant, speed.

light speed (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