" things, that while not identical, can be used interchangeably." -- Wheat, for example, is a fungible commodity. If you're a trader, any freightcar-ful is the same as any other. Lawyers have nothing to do with it.

The root also has stalks that are even more commonplace. Isn't a "fungo bat," used by baseball coaches to hit fly balls to the outfielders for warm-up, called that because it doesn't really matter which bat is used? Bats are fungible, at least for this purpose.