1940, from of German Panzerdivision "armored unit," from Panzer "tank," literally "armor," from Middle High German panzier, from Old French panciere "armor for the belly," from pance "belly, stomach," from Latin pantex (genitive panticis) "belly" (see paunch).
late 14c. paunce, "the human belly," from Old French pance (Old North French panche) "belly, stomach," from Latin panticem (nominative pantex) "belly, bowels" (source also of Spanish panza, Italian pancia); which is possibly related to panus "swelling" (see panic (n.2)). Earlier in English it meant "plate or mail armor worn to protect the belly" (early 14c.).
c. 1300, perhaps from Middle Low German *smilen or a Scandinavian source (such as Danish smile "smile," Swedish smila "smile, smirk, simper, fawn"), from Proto-Germanic *smil-, extended form of PIE root *smei- "to laugh, smile" (source also of Sanskrit smayate "smiles;" Latvian smiêt "to laugh;" Latin mirus "wonderful," mirari "to wonder;" Old English smerian "to laugh at, scorn," Old High German smieron "to smile"). Related: Smiled; smiling.
It gradually pushed the usual Old English word, smearcian (modern smirk), into a specific, unpleasant sense. Of the eyes, from 1759. Figuratively, as indicating favor or encouragement, from c. 1400. Romance, Celtic, and Slavic languages tend to use a diminutive of the word for "laugh" to mean "smile" (such as Latin ridere "laugh;" subridere "smile"), perhaps literally "small laugh" or "low laugh."
late 14c., "small chamber or cavity within a bodily organ," especially of the heart, from Latin ventriculus (in reference to the heart, ventriculus cordis), literally "little belly," diminutive of venter (genitive ventris) "belly" (see ventral).
having a swelling or hollow middle, late 15c., from belly (n.). From 1590s as "puffed out." Also, since 16c., in compounds, "having a belly" of a specified kind.
Old English midhrif "diaphragm of a human or animal," from mid "mid" (from PIE root *medhyo- "middle") + hrif "belly," from Proto-Germanic *hrefin (source also of Old High German href, Old Frisian hrif, -rith, -rede "belly"). Compare Old Frisian midrede "diaphragm." Watkins has this from PIE root *kwrep- "body, form, appearance;" Boutkan has it from *sker- (1) "to cut."
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.