The Collaborative International Dictionary of English v.0.48:

Kosher \Ko"sher\, a. [heb. kosh["e]r fit, proper.]
   1. Ceremonially clean, according to Jewish law; -- applied to
      food, esp. to meat of animals slaughtered according to the
      requirements of Jewish law. Opposed to tref. For food to
      be officially kosher, it must be certified fit to eat by a
      Rabbi, according to Jewish ritual law; as, kosher food.
      Hence, designating a shop, store, house, etc., where such
      food is sold or used; as, a kosher restaurant.

   Syn: cosher, ritually fit, sanctioned.
        [Webster 1913 Suppl.]

   2. Hence: Proper; seemly; appropriate; legitimate; as, it's
      not kosher to do it that way. [colloq.]
      [PJC]

   3. Genuine. [colloq.]
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Kosher \Ko"sher\, n.
   Kosher food; also, a kosher shop.
   [Webster 1913 Suppl.]

   2. the practise of adherence to the Jewish ritual law; used
      mostly in the phrase

   keep kosher, v. i..
      [PJC]

   keep kosher To adhere to the rules for eating only kosher
      food and handling it properly.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Kosher \Ko"sher\, v. t. [imp. & p. p. Koshered; p. pr. & vb.
   n. Koshering.]
   To prepare in conformity with the requirements of the Jewish
   law, as meat.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

kosher
    adj 1: conforming to dietary laws; "kosher meat"; "a kosher
           kitchen" [syn: kosher, cosher]
    2: proper or legitimate
    n 1: food that fulfills the requirements of Jewish dietary law

Moby Thesaurus II by Grady Ward, 1.0:

113 Moby Thesaurus words for "kosher":
   accordant, according to Hoyle, actionable, anal, applicable,
   appropriate, authorized, bleached, bourgeois, bright, clean,
   cleanly, comestible, competent, compulsive, concordant, condign,
   conformist, constitutional, conventional, correct, corresponding,
   dainty, decent, decorous, delicious, dirt-free, due, eatable,
   edible, esculent, fair, fastidious, fit, fitting, formalistic,
   fresh, good, gustable, harmonious, immaculate, in accord,
   in keeping, in line, in step, judicial, juridical, just,
   justiciable, lawful, lawmaking, legal, legislative, legit,
   legitimate, licit, nice, nonpolluted, normal, normative,
   of cleanly habits, orthodox, palatable, pedantic, plastic,
   precisianistic, proper, pure, right, right and proper, righteous,
   rightful, ritually pure, sanctioned, savory, seemly, shiny,
   smut-free, smutless, spotless, square, stainless, statutory,
   straight, stuffy, succulent, suitable, sweet, tahar,
   traditionalist, tubbed, unadulterated, unbesmirched, unblemished,
   unblotted, undefiled, unmuddied, unpolluted, unsmirched, unsmudged,
   unsoiled, unspotted, unstained, unsullied, untainted, untarnished,
   uptight, valid, well-scrubbed, well-washed, white, whitened,
   within the law