Source : Webster's Revised Unabridged Dictionary (1913)

Tan \Tan\, v. t. [imp. & p. p. {Tanned}; p. pr. & vb. n.
   {Tanning}.] [F. tanner, LL. tannare. See {Tan}, n.]
   1. To convert (the skin of an animal) into leather, as by
      usual process of steeping it in an infusion of oak or some
      other bark, whereby it is impregnated with tannin, or
      tannic acid (which exists in several species of bark), and
      is thus rendered firm, durable, and in some degree
      impervious to water.

   Note: The essential result in tanning is due to the fact that
         the tannins form, with gelatins and albuminoids, a
         series of insoluble compounds which constitute leather.
         Similar results may be produced by the use of other
         reagents in place of tannin, as alum, and some acids or
         chlorides, which are employed in certain processes of
         tanning.

   2. To make brown; to imbrown, as by exposure to the rays of
      the sun; as, to tan the skin.

Tanning \Tan"ning\, n.
   The art or process of converting skins into leather. See
   {Tan}, v. t., 1.

Source : WordNet®

tan
     adj : of a light yellowish-brown color
     [also: {tanning}, {tanned}, {tannest}, {tanner}]

tanning
     n 1: process in which skin pigmentation darkens as a result of
          exposure to ultraviolet light
     2: beating with a whip or strap or rope as a form of punishment
        [syn: {whipping}, {flogging}, {lashing}, {flagellation}]
     3: making leather from rawhide

tan
     n 1: a browning of the skin resulting from exposure to the rays
          of the sun [syn: {suntan}, {sunburn}, {burn}]
     2: a light brown [syn: {topaz}]
     3: ratio of the opposite to the adjacent side of a right-angled
        triangle [syn: {tangent}]
     [also: {tanning}, {tanned}, {tannest}, {tanner}]

tan
     v 1: treat skins and hides with tannic acid so as to convert them
          into leather
     2: get a tan, from wind or sun [syn: {bronze}]
     [also: {tanning}, {tanned}, {tannest}, {tanner}]

tanning
     See {tan}