The Collaborative International Dictionary of English v.0.48:

Gastric \Gas"tric\, a. [Gr. ?, ?, stomach: cf. F. gastrique.]
   Of, pertaining to, or situated near, the stomach; as, the
   gastric artery.
   [1913 Webster]

   Gastric digestion (Physiol.), the conversion of the
      albuminous portion of food in the stomach into soluble and
      diffusible products by the solvent action of gastric
      juice.

   Gastric fever (Med.), a fever attended with prominent
      gastric symptoms; -- a name applied to certain forms of
      typhoid fever; also, to catarrhal inflammation of the
      stomach attended with fever.

   Gastric juice (Physiol.), a thin, watery fluid, with an
      acid reaction, secreted by a peculiar set of glands
      contained in the mucous membrane of the stomach. It
      consists mainly of dilute hydrochloric acid and the
      ferment pepsin. It is the most important digestive fluid
      in the body, but acts only on proteid foods.

   Gastric remittent fever (Med.), a form of remittent fever
      with pronounced stomach symptoms.
      [1913 Webster]

WordNet (r) 3.0 (2006):

gastric
    adj 1: relating to or involving the stomach; "gastric ulcer"
           [syn: gastric, stomachic, stomachal]

Moby Thesaurus II by Grady Ward, 1.0:

24 Moby Thesaurus words for "gastric":
   abdominal, anal, appendical, big-bellied, cardiac, cecal, celiac,
   colic, colonic, coronary, duodenal, enteric, ileac, intestinal,
   jejunal, mesogastric, pyloric, rectal, splanchnic, stomachal,
   stomachic, ventral, ventricular, visceral