midriff (n.)

Old English midhrif, from mid "mid" (from PIE root *medhyo- "middle") + hrif "belly," from Proto-Germanic *hrefiz- (source also of Old High German href, Old Frisian hrif "belly"), from PIE root *kwrep- "body, form, appearance." More or less obsolete after 18c. except in phrase to tickle (one's) midriff "to cause laughter;" the word revived 1941 in fashion usage for "portion of a woman's garment that covers the belly," as a euphemistic avoidance of belly; sense inverted and extended 1970 to a belly-baring style of women's top.