The Collaborative International Dictionary of English v.0.48:
Pyrosis \Py*ro"sis\, n. [NL., fr Gr. ? a burning, an inflammation, fr. ? to burn, fr. ? fire.] (Med.) See Water brash, under Brash. [1913 Webster]WordNet (r) 3.0 (2006):
pyrosis n 1: a painful burning sensation in the chest caused by gastroesophageal reflux (backflow from the stomach irritating the esophagus); symptomatic of an ulcer or a diaphragmatic hernia or other disorder [syn: heartburn, pyrosis]