Historically, the second crewman in a Royal Navy aircraft is an "Observer" - possibly from their early rôle observing the fall of shot? Their job, though, was to do everything that wasn't the physical poling about of the aircraft, from telling the Boss where to go to managing all the radio communications to supervising the letting go of most of the weapons, the pilot being just some kind of three-dimensional chauffeur. Indeed, in the early days, I think Observers could have been superior in rank to pilots, and in charge of the aircraft.
However "everything-else-officer" sounds un-naval and "aircraft manager" is just a cop-out. More recently "Weapons System Operator" covers a lot of ground, but leaves out the Navigational aspects. The third crewamn in a Swordfish, for instance, was a Telegraphist/Air Gunner while the Observer is, yet again, the everything-else-officer.
The case for the RAF is just as bad, "Navigator" covering only a little of what the second man actually does.
This division of labour is emphasised by the fact that in aircraft such as Sea Vixen, TSR-2 or B-58 the second man *does not need to see out* and has only a porthole to let a bit of light in. His job is entirely involved with managing the aircraft.
The "coal-hole" reference comes from the provision in many British homes that were still heated by solid fuel of a "coal-hole" in front of the house down which coal was delivered into a pit in the cellar, without bringing it through the house, to keep the coal dust under control. Inside, coal would be shovelled out through a small hole in the bottom of the coal-hole pit, and brought up when needed.
In the Sea Vixen, the Observer got in through the top hatch into a small black hole with the occasional thing that glittered. I don't think it was an affectionate nickname.