What is the equivalent of sub-/supersonic for the speed of light?
We have subsonic and supersonic for speeds below or above the speed of sound. What is the equivalent for the speed of light?
I've seen superluminal and subluminal. Sometimes sub-lightspeed
Particularly if you are referring to particles, you could use tachyonic for faster-than-light and bradyonic for slower-than-light.
For speeds below the speed of light, you can consider the word sublight http://stargate.wikia.com/wiki/Sublight_engine
For speeds above the speed of light, you can consider F.T.L., meaning faster-than-light. See here