- Wood used for military materiel, especially in the context of historical warfare
war + wood. Perhaps at least partly an allusion to koa (Acacia koa on Wikipedia.), a tree endemic to Hawaii with wood similar in quality to black walnut, and whose name in Hawaiian can also mean warrior, or to beefwood (Casuarina equisetifolia on Wikipedia.) which also has deep-colored, hard wood and in some Polynesian languages shares the same association between the name and words for warriors (both cognate with the Hawaiian term).