Englishvelocity
noun
light always travels at the same constant velocity:
speed, pace, rate, tempo, momentum, impetus;
swiftness, swift/fast pace, fastness, quickness, speediness, rapidity, briskness, expeditiousness, expedition, dispatch;
acceleration;
informal clip, fair old rate, fair lick, steam, nippiness;
literary fleetness, celerity.
velocity Oxford Dictionary of English