Wiktionary
n. (context science fiction English) A fictional beam of radiation that can kill.
Wikipedia
Death Ray was a British magazine devoted to science fiction and fantasy in all its forms, especially media-related topics and novels. It was published every two months, with the first issue going on sale in May 2007. Typical issues were 132 pages, perfect bound, on glossy paper.
The death ray or death beam was a theoretical particle beam or electromagnetic weapon of the 1920s through the 1930s that was claimed to have been invented independently by Guglielmo Marconi, Nikola Tesla, Harry Grindell Matthews, Edwin R. Scott, and Graichen, as well as others. In 1957, the National Inventors Council was still issuing lists of needed military inventions that included a death ray.
While based in fiction, research into energy-based weapons inspired by past speculation has contributed to real-life weapons in use by modern militaries sometimes called a sort of "death ray", such as the United States Navy and its Laser Weapon System (LaWS) deployed in mid-2014. Such armaments are technically known as directed-energy weapons.
Usage examples of "death ray".
In some uncanny fashion, the ex-neutralizer had become a death ray.
If only Zaretsky could be persuaded by some ruse that Blanovich and the death ray were gone from the chalet, he'd no longer have reason to drop explosives.
Later he wrote the even more obvious Engineer Garin and his Death Ray, in which a fanatical communist scientist defeats and rules the USA.
They have that death ray, but it's not quite as deadly as we might have feared, solely because our ships could outmaneuver them.