Yes, there is a range, but I don’t know of a strict definition. I would recommend a very interesting paper on the topic (CJ Bartleson, Brown, Color Res. Appl. 1, 181-191 (1976)) that includes scaling of brown and defines the boundaries of brown in Munsell space. You could also just have a few people look at samples and estimate boundaries yourself. You might also take a look at the “ISCC-NBS Dictionary of Color Names.” It is out of print, but an internet search may find copies.