Brownies

Brownies are one of the lesser spirits appearing in 'The Book of Lost Tales.

Background
Brownies were among the sprites of trees and woods, of dale and forest and mountain-side, or those who sung amid the grass and chant among the standing corn at eve. These races and a number of others besides (Tavari, Nandini and Orossi,  fays, pixies, and leprawns and what else they were called) shared the world in a time before the coming of the Eldar, and before world (where music of the ainur began, the Timeless Halls).

Behind the scenes
John Rateliff notes;

...drawn attention to, the appearance of brownie here, for the brownies or brown-men of traditional folk-lore are a kind of hob. And, since we have every reason to believe Tolkien drew on hob-lore when creating his hobbits more than a decade later, it's of interest to find a hint of some kind of similar creature within his mythology, albeit in a much different role, at a much earlier stage. I don't think we can make too much of this, but it does at least open the possibility that when Tolkien sat down in the summer of 1930 and spontaneously invented his hobbits he had already potentially made a place for them within his legendarium long before. And we can't rule out that he thought of hobbits along those earlier lines when he first set out to tell Bilbo's story, however greatly they diverged in the telling.

So, if there's ever a second edition of THE HISTORY OF THE HOBBIT, I'll need to add a paragraph or so to that effect drawing attention to this passage to what's now JDR Note 1 on page 850 of RETURN TO BAG-END.