Phaser

Phasers were energy weapons which could stun or kill, depending on their power settings. (PROSE: Mindwarp)

In one occasion, the Fourth Doctor complained about always meeting people "pointing guns or phasers or blasters" during his travels across the universe. (TV: The Horns of Nimon)

In 2379, "CD phasers" were sold to Thordon, where the Sixth Doctor got one exemplar from a Warlord; this occurrence led him to their source, Thoros Beta. There, indeed, it was widely employed by the subordinates of Kiv, leader of the Mentors. Eventually, in a timeline, King Yrcanos killed Peri Brown with a phaser (called "liquifier" by him) as an act of mercy after her body was possessed by Kiv. (TV: Mindwarp)

While facing the threat of the Vervoids on the Hyperion III, the Sixth Doctor asked for a phaser, arousing the astonishment of his companion Melanie Bush. He secretly disarmed it, so later Doland couldn't use it against him. (TV: Terror of the Vervoids)

In a parallel universe, a kind of phaser was used aboard the USS Enterprise. In 2368, it proved to be ineffective against the Cybermen. (COMIC: Assimilation²)