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.
Faster than light has to be Warp speed. Everything else is just normal, impulse power.