Tolkien got this term from the legendary Woodwoses.
The Drûgin lived among the Second House of Men, the Haladin, in the First Age in the forest of Brethil. They were an alien folk to the other Men: a bit like Dwarves in stature and endurance, stumpy, clumsy-limbed (with short, thick legs, and fat, "gnarled" arms), had broad chests, fat bellies, and heavy buttocks. According to the Elves and other Men, they had "unlovely faces": wide, flat, and expressionless with deep-set black eyes that glowed red when angered. They had "horny" brows, flat noses, wide mouths, and sparse, lanky hair. They had no hair lower than the eyebrows, except for a few men who had a tail of black hair on the chin. Although a number of the Drúedain were present in Númenor they had left or died out before the Akallabêth, as had the Púkel-men of Dunharrow. At the end of the Third Age the Drûg still lived in the Drúadan Forest of the White Mountains, and at the long cape of Andrast west of Gondor. The region north of Andrast was still known as Drúwaith Iaur, or "Old Drûg land".
The Woses of Ghân-buri-Ghân held off Orcs with poisoned arrows and were vital in securing the aid of the Rohirrim in the Battle of the Pelennor Fields. King Elessar granted the Drúadan Forest "forever" to them in the Fourth Age.