late 14c. variant of earlier stomake (early 14c.), "internal pouch into which food is digested," from Old French stomaque, estomac "stomach," from Latin stomachus "throat, gullet; stomach," also "taste, inclination, liking; distaste, dislike;" also "pride, indignation," which were thought to have their origin in that organ (source also of Spanish estómago, Italian stomaco), from Greek stomachos "throat, gullet, esophagus," literally "mouth, opening," from stoma "mouth" (see stoma).
Applied anciently to the openings of various internal organs, especially that of the stomach, then by the later Greek physicians to the stomach itself. The native word is maw (Old English maga glosses stomachus).
Some 16c. anatomists tried to correct the sense back to "esophagus" and introduce ventricle for what we call the stomach. Meaning "belly, midriff, part of the body that contains the stomach" is from late 14c.
In Middle English also stomack, stomac, stommak, stomoke; the spelling of the ending of the word was conformed to Latin regularly from 16c., but the pronunciation remains as in Middle English. Related: stomachial (1580s); stomachical (c. 1600); stomachic (1650s). Pugilistic stomacher "punch in the stomach" is from 1814; from mid-15c. as "vest or other garment which covers the belly." The Latin figurative senses also were in Middle English (such as "relish, inclination, desire," mid-15c.) or early Modern English. Also sometimes regarded in Middle Ages as the seat of sexual desire.