Coal Mine Slangs

I'm one lump short of a coal mine

What does it mean?

Ans: (Old timer's slang): It means that a person is very valuable as a natural resource (eg coal mine), but they are just short of a valuable ingredient. A lump of coal, which may have turned to diamond over a period of time and had been removed from the mine.

The saying is often seen on T-shirts, hats, ever since coal is beginning to have a resurgence in the US energy markets.