Emily Dickinson Lexicon

TAN, v.t. [Fr. tanner, to tan; tanne, a little black spot on the face; It. tane, tawny color. Gregoire, in his Armoric dictionary, suggests that this may be from tan or dan, which in Leon signifies an oak. But this is very doubtful. In Ir. tionus signifies a tan-house, and tionsonaim, is to drop or distill. Spotting is often from sprinkling, and dyeing from dipping. In Gaelic, dean is color. It seems to be allied to tawny, and perhaps to dun.]

1. In the arts, to convert animal skins into leather by steeping them in an infusion of oak or some other bark, by which they are impregnated with tannin or tannic acid, an astringent substance which exists in several species of bark, and thus rendered firm, durable, and in some degree, impervious to water.
2. To make brown; to imbrown by exposure to the rays of the sun; as, to tan the skin. His face all tann'd with scorching sunny rays. Spenser.