keep kosher

from 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]