The Collaborative International Dictionary of English v.0.48:

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.
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The Collaborative International Dictionary of English v.0.48:

Sallow \Sal"low\, v. t.
   To tinge with sallowness. [Poetic]
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         July breathes hot, sallows the crispy fields. --Lowell.
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The Collaborative International Dictionary of English v.0.48:

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.
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            And bend the pliant sallow to a shield. --Fawkes.
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            The sallow knows the basketmaker's thumb. --Emerson.
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   2. (Bot.) A name given to certain species of willow,
      especially those which do not have flexible shoots, as
      Salix caprea, Salix cinerea, etc.
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   Sallow thorn (Bot.), a European thorny shrub (Hippophae
      rhamnoides) much like an Elaeagnus. The yellow berries
      are sometimes used for making jelly, and the plant affords
      a yellow dye.
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WordNet (r) 3.0 (2006):

sallow
    adj 1: unhealthy looking [syn: sallow, sickly]
    n 1: any of several Old World shrubby broad-leaved willows
         having large catkins; some are important sources for
         tanbark and charcoal
    v 1: cause to become sallow; "The illness has sallowed her face"

Moby Thesaurus II by Grady Ward, 1.0:

99 Moby Thesaurus words for "sallow":
   achromatic, achromic, anemic, ashen, ashy, aureate, auric, beige,
   bled white, bloodless, buff, buff-yellow, cadaverous, canary,
   canary-yellow, chloranemic, citron, citron-yellow, colorless,
   cream, creamy, dead, deadly pale, deathly pale, dim, dimmed, dingy,
   discolored, dull, exsanguinated, exsanguine, exsanguineous, faded,
   faint, fallow, flat, flaxen, ghastly, gilded, gilt, gold,
   gold-colored, golden, gray, haggard, hueless, hypochromic,
   icterous, jaundiced, lackluster, leaden, lemon, lemon-yellow,
   livid, lurid, lusterless, luteolous, lutescent, mat, mealy, muddy,
   neutral, ocherish, ocherous, ochery, ochreous, ochroid, ochrous,
   ochry, or, pale, pale as death, pale-faced, pallid, pasty,
   primrose, primrose-colored, primrose-yellow, saffron,
   saffron-colored, saffron-yellow, sand-colored, sandy, sickly,
   straw, straw-colored, tallow-faced, toneless, uncolored, wan,
   washed-out, waxen, weak, whey-faced, white, xanthic, xanthous,
   yellow, yellowish