Source : Webster's Revised Unabridged Dictionary (1913)

Sallow \Sal"low\ (s[a^]l"l[-o]), n. [OE. salwe, AS. sealh; akin
   to OHG. salaha, G. salweide, Icel. selja, L. salix, Ir. sail,
   saileach, Gael. seileach, W. helyg, Gr. "eli`kh.]
   1. The willow; willow twigs. [Poetic] --Tennyson.

            And bend the pliant sallow to a shield. --Fawkes.

            The sallow knows the basketmaker's thumb. --Emerson.

   2. (Bot.) A name given to certain species of willow,
      especially those which do not have flexible shoots, as
      {Salix caprea}, {S. cinerea}, etc.

   {Sallow thorn} (Bot.), a European thorny shrub ({Hippophae
      rhamnoides}) much like an El[ae]agnus. The yellow berries
      are sometimes used for making jelly, and the plant affords
      a yellow dye.

Sallow \Sal"low\, a. [Compar. {Sallower}; superl. {Sallowest}.]
   [AS. salu; akin to D. zaluw, OHG. salo, Icel. s["o]lr
   yellow.]
   Having a yellowish color; of a pale, sickly color, tinged
   with yellow; as, a sallow skin. --Shak.

Sallow \Sal"low\, v. t.
   To tinge with sallowness. [Poetic]

         July breathes hot, sallows the crispy fields. --Lowell.

Source : WordNet®

sallow
     adj : unhealthy looking [syn: {sickly}]
     n : any of several Old World shrubby broad-leaved willows having
         large catkins; some are important sources for tanbark and
         charcoal

sallow
     v : cause to become sallow; "The illness has sallowed her face"