Wiktionary
sub-light
a. (context science fiction English) At less than the speed of light. alt. (context science fiction English) At less than the speed of light.
Usage examples of "sub-light".
But it seemed long, until the sub-light detectors bleeped, and told him that the Deux was safely below C.
Of course, now that they're traveling at sub-light speed, their fuel consumption rate has gone down ….
Erica LeMay came up with a scheme to give us power in the sub-light engines.
Retribution took a hit that damaged sub-light engines, and we had to lay up for a day.