It was noted as one of the killing gifts allowing an individual to kill with just their minds. A rare ability, the Killing Thought came randomly every few generations though the breeding of two Vulcans with the gift allowed it to be passed onto their child. A danger with those who have the Killing Thought technique was that undisciplined minds tended to accidentally kill people through the technique.
During the years before the Vulcan Reformation, the Lady Suvin attempted to breed the gift through a child of another House and bonded her to her grandson in the attempt to gain a weapon. Her goals was to get a great-grandchild with the Last Thought technique which she could use against her enemies. (TOS novel: Spock's World)