We know the fighter-mage is called a gish, but what about a fighter-rogue? A mage-rogue?
Thug for fighter/rogue.
Arcane Trickster for mage/rogue.
Edit:
A fighter-rogue is called a Ranger or Scout.
Right, a very good answer too. Swashbuckler works here too.
A Mage-rogue would be called suboptimal, I suspect.
Yes, but see Unseen Seer, getting twice as much sneak attack as a normal rogue via spells and class features while having 19th or 20th level wizard casting is tech.
Edit2: Tshern Ninjaed my edit