Remember the searches for "conventional" dark matter?
After all the WIMPs, someone had to come up with MACHOs. Extensive searches were made for dark objects roaming the interstellar space, by watching for microlensing events within our Galaxy (or involving stars in the satellite galaxies such as the Magellanic Clouds).
In the papers describing these efforts, one class of proposed objects were "rogue planets" (not rogue exoplanets) and, apparently, no one had any problem with the phrase.
Of course, that is a moot point, since they did not find anything smaller than brown dwarfs.
However, some of these objects have been recently discovered (10-Jupiter-Mass objects) and the article I just read uses the phrase "unbound planets"
"Bound and unbound planets abound" by Joachim Wambsganss. Nature, v.473, pp.289-291 (19 May 2011)