The story
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).
Etymology from Wiktionary, CC BY-SA 4.0.
ploonet
Today it means: 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. Full definition →