Rogue rocketed to the top of our lookups on October 15th, 2018, following President Trump’s musings, in which he wielded the word as an adjective modifying killers, on the possible identity of journalist Jamal Khashoggi’s murderers.
President Trump raised the possibility on Monday that “rogue killers” were behind the disappearance of a Saudi dissident journalist as the kingdom prepared to admit Jamal Khashoggi was killed in an interrogation gone wrong, according to a person familiar with the Saudi plans.
— Eileen Sullivan and David D. Kirkpatrick, The New York Times, 15 Oct. 2018
Rogue has functioned as a noun since the 15th century, and a verb (not very commonly used) since the 18th. The adjective use is the newest of them all, dating from the first half of the 19th century. In this part of speech it was initially applied to elephants and is still defined with the sense "resembling or suggesting a rogue elephant especially in being isolated, aberrant, dangerous, or uncontrollable." The etymology of the word is unknown.
A rogue elephant is either a large male, who has been driven from the herd, after losing a contest for the mastery of the whole; or a female, wandering from it in quest of her calf.
— The Guardian (London, Eng.), 18 Apr. 1835
