Sentence:  The Gabriel pointed towards her destination and , under one gee acceleration , began to build up towards her ultimate velocity , 99.1 percent of the <WSD>speed</WSD> of light . 
Meaning of the word marked with <WSD> tags:  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