The Collaborative International Dictionary of English v.0.48:

Gravy \Gra"vy\, n.; pl. Gravies. [OE. greavie; prob. fr.
   greaves, graves, the sediment of melted tallow. See
   Greaves.]
   1. The juice or other liquid matter that drips from flesh in
      cooking, made into a dressing for the food when served up.
      [1913 Webster]

   2. Liquid dressing for meat, fish, vegetables, etc.
      [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

60 Moby Thesaurus words for "gravy":
   Colbert, Smitane, Soubise, Trinkgeld, allemande, bonus,
   bonus system, bounty, bourguignonne, bribe, brown sauce,
   buried treasure, consideration, cream sauce, discovery, donative,
   double time, egg sauce, espagnole, fee, find, finding, foundling,
   fringe benefit, gratuity, grease, honorarium, incentive pay,
   inducement, lagniappe, largess, liberality, marinara, mole,
   overtime pay, palm oil, paprika sauce, pepper sauce, perks,
   perquisite, perquisites, poulette, pourboire, premium, roux, salve,
   shallot sauce, solatium, something extra, sportula, sweetener, tip,
   treasure trove, trouvaille, trove, waifs, waifs and strays,
   windfall, windfall money, windfall profit