Sentence:  A <WSD>gravitational-wave</WSD> detector exploits the physical effects of a <WSD>gravitational wave</WSD> on bodies to detect the waves. A <WSD>gravitational wave</WSD> detector may, for example, monitor the separation between two freely falling bodies; as a <WSD>gravitational wave</WSD> passes, the two bodies will experience a tidal acceleration relative to each other. 
Meaning of the word marked with <WSD> tags:  A fluctuation in spacetime caused by accelerating mass, which propagates as a wave at the speed of light.