Wiktionary
alt. An early radio receiver, having no electrical power supply except the radio waves themselves; it used a crystal of lead or cadmium sulphide and a wire (the ''cat's whisker'') touching the crystal's surface. n. An early radio receiver, having no electrical power supply except the radio waves themselves; it used a crystal of lead or cadmium sulphide and a wire (the ''cat's whisker'') touching the crystal's surface.
WordNet
n. an early radio receiver using a crystal detector
Usage examples of "crystal set".
There's a crystal set into the back of the wall, crafted to absorb any form of probing and return an image of impenetrable rock.
He hesitated and looked over at the small communications crystal set in the mount next to the heavy weapon.
It was some sort of rock crystal set up underneath the dome in a stone frame.