Nautical... glad I could help. It's just Uncle that's slang for pawnbroker (people used to say they were going to 'see uncle', less indicative of their poverty!). Yes, I knew 'carbuncle' as a festering sore, and have always found it strange that it has the other meaning, a gem.
Grunger, thanks. I'm relieved that you've got a satisfactory explanation. In this case - as often happens for me - I find the correctness of the answer easier to recognise than to define!