Planetes (πλανήτης) means a wanderer, specifically used in the New Testament to describe wandering stars. The word is the source of the English word "planet." In its sole NT occurrence (Jude 13), it is used metaphorically to describe false teachers — they are like stars that have left their appointed course, wandering without fixed orbit, destined for eternal darkness.
Jude employs a series of powerful nature metaphors to expose false teachers: they are "waterless clouds," "fruitless trees," "wild waves of the sea," and finally "wandering stars, for whom the gloom of utter darkness has been reserved forever." The metaphor of a wandering star is particularly evocative. In the ancient world, fixed stars were reliable for navigation; a wandering star was unreliable and misleading. False teachers appear luminous but lead people off course. The phrase "blackest darkness forever" echoes 2 Peter 2:17 and underscores the severity of judgment awaiting those who corrupt the faith. This single-use word carries enormous theological weight as a warning against spiritual charlatans.