A spade, we are told, is a spade, and not to be confused with a shovel. 

Hah! 

The common garden spade, as it evolved in Europe and particularly in England, has a blade that is a rectangle. (Photo of different types of shovels offered.)

The digging shovel so ubiquitous here in the U.S.A. has a blade shaped exactly like a spade. (Just compare your shovel, head up, to any deck of cards.)

Go figure. 

Shapes aside, the primary difference between ...