gastrolith Syllabification: (gas·tro·lith)Pronunciation: /ˈgastrəˌliTH/Definition of gastrolith noun 1 Medicine a hard concretion in the stomach. 2 Zoology a small stone swallowed by a bird, reptile, or fish, to aid digestion in the gizzard. gastrolith in other Oxford dictionaries Definition of gastrolith in the British & World English dictionary