Though I don't yet know how you guys feel about bringing in an idea from another fictional universe, "ion engine" is an issue for Star Wars fans, too.
As a form of propulsion it sucks (because of the energy you have to invest to accelerate the exhaust particles), you can only operate it in the vacuum of space and Darth Vader's long-range "Twin Ion Engine" fighter obviously just doesn't have two but four sublight propulsion engines.
Again, I think we are looking at a colloquialism that refers to a nuclear fusion reactor that foremost produces energy (like a "steam engine" produces the mechanical energy to propel a locomotive) and "ions" is what it's working with.
In theoretical propulsion considerations the "fusion rocket" would be best as the particle exhaust velocity is superior to all the others "known" to our science. Simply put it's a fusion reactor with an exhaust nozzle.
If you could put such a fusion reactor into a shuttlecraft you'd always be facing a dilemma: Use the energy for antigrav liftoff and/or FTL drive or
use it as a conventional form of propulsion for sublight thrust.
TOS has a great illustration of that dilemma in "Balance of Terror". The Romulan commander always has to decide whether to use his "fuel" to produce energy for the cloaking device or to use it for propulsion thrust.