A guillotine was a capital punishment device that decapitated the victim.
The Clown, a manifestation of fear who was accidentally created in Viorsa's artificial environment, used a pink guillotine to metaphorically decapitate people. Because he was part of a computer that monitored and controlled participants' vital signs, he used the extreme stress levels that accompany fear to induce heart attacks and thereby kill his victims despite the fact that he was non-corporeal. The Clown executed two members of Viorsa's species before the arrival of Harry Kim and B'Elanna Torres, and during a subsequent escape attempt, he also executed Viorsa. (VOY: "The Thaw")