The word "gastroxynsis" refers to the muscular contraction of the stomach. In terms of its spelling, it is pronounced /ɡæstroʊksaɪnsɪs/ with the stress on the second syllable. The "gastro" prefix is derived from the Greek word for stomach, while "xynsis" refers to contraction. The spelling of this word can be tricky because of the "x" and "y" sounds in the middle, but it can be remembered by separating the word into its root parts and pronouncing each one clearly.
Intermittent hyperchlorhydria.
A practical medical dictionary. By Stedman, Thomas Lathrop. Published 1920.