ploonet
A theoretical planetary body that formed as a moon orbiting a planet, but which has become tidally detached, so that it enters orbit about its star, separated from its parent planet.
This paper explores the scenario where large regular exomoons escape after tidal interchange of angular momentum with its parent planet, becoming small planets by themselves. We name this hypothetical type of object a ploonet.
Where it comes from
Blend of planet + moon. Coined in 2019 by the research team of Mario Sucerquia, Jaime A Alvarado-Montes, Jorge I Zuluaga, Nicolás Cuello, Cristian Giuppone (see quotations below).
Adapted from the Wiktionary entry ploonet (CC BY-SA 4.0).