The crushed bark of the oak or of other trees, an infusion of which is used in converting hides into leather.
The powdered bark of an oak tree, used in tanning.
The inner bark of the American black oak, Quercus velutina, used as a source of the yellow dye quercitrin and in tanning (more fully quercitron bark)…
The cork oak, Quercus suber. Also: the bark of this, formerly used in tanning and occasionally medicinally. Now rare.