I thought there was a term for it - "Rogue planets"
Ok, so if it wasn't orbiting a star, ever, then call it a sub-brown dwarf.
Seems fine to me.
Wikipedia Wrote:A rogue planet (also known as an interstellar planet, or orphan planet) is a planetary-mass object that has been ejected from its system and is no longer gravitationally bound to any star, brown dwarf or other such object, and that therefore orbits the galaxy directly.[1][2][3] Astronomers estimate that there are twice as many Jupiter-sized rogue planets as there are stars.[4]
Isolated planetary-mass objects which were not ejected, but have always been free-floating, are thought to have formed in a similar way to stars, and the IAU has proposed that those objects be called sub-brown dwarfs.[5]]
Ok, so if it wasn't orbiting a star, ever, then call it a sub-brown dwarf.
Seems fine to me.