The Collaborative International Dictionary of English v.0.48:

Sirup \Sir"up\Syrup \Syr"up\, n. [F. sirop (cf. It. siroppo, Sp.
   jarabe, jarope, LL. siruppus, syrupus), fr. Ar. shar[=a]b a
   drink, wine, coffee, sirup. Cf. Sherbet.]
   1. A thick and viscid liquid made from the juice of fruits,
      herbs, etc., boiled with sugar.
      [1913 Webster]

   2. A thick and viscid saccharine solution of superior quality
      (as sugarhouse sirup or molasses, maple sirup);
      specifically, in pharmacy and often in cookery, a
      saturated solution of sugar and water (simple sirup), or
      such a solution flavored or medicated.
      [1913 Webster]

            Lucent sirups tinct with cinnamon.    --Keats.
      [1913 Webster]

   Mixing sirup. See the Note under Dextrose.
      [1913 Webster] Siruped

The Collaborative International Dictionary of English v.0.48:

Syrup \Syr"up\, n., Syrupy \Syr"up*y\, a. [See Sirup.]
   Same as Sirup, Sirupy.
   [1913 Webster]

WordNet (r) 3.0 (2006):

syrup
    n 1: a thick sweet sticky liquid [syn: syrup, sirup]

Moby Thesaurus II by Grady Ward, 1.0:

122 Moby Thesaurus words for "syrup":
   adherent, adhesive, albumen, ambrosia, artificial sweetener, balm,
   balsam, barnacle, batter, blackstrap, bonnyclabber, bramble, brier,
   bulldog, burr, butter, calcium cyclamate, cane syrup, cement,
   clabber, clover honey, comb honey, corn syrup, cornstarch, cream,
   curd, cyclamates, decal, decalcomania, dough, drops, drug,
   edulcoration, egg white, electuary, elixir, ethical drug, gaum,
   gel, gelatin, generic name, glair, glop, glue, gluten, goo, gook,
   goop, gruel, gumbo, gunk, herbs, honey, honeycomb, honeydew,
   honeypot, inhalant, jam, jell, jelly, leech, limpet, lincture,
   linctus, loblolly, maple syrup, materia medica, medicament,
   medication, medicinal, medicinal herbs, medicine, mixture,
   molasses, mucilage, mucus, nectar, nonprescription drug, officinal,
   pap, paste, patent medicine, pharmacon, physic, plaster, porridge,
   powder, preparation, prescription drug, prickle, proprietary,
   proprietary medicine, proprietary name, pudding, pulp, puree,
   putty, remora, rob, saccharification, saccharin, semifluid,
   semiliquid, simples, size, sodium cyclamate, sorghum, soup, starch,
   sticker, sticky mess, sugar, sugar-making, sugaring off, sweetener,
   sweetening, sweets, theraputant, thorn, tisane, treacle,
   vegetable remedies