late 14c., "jaw, jawbone," from Middle French mandible and directly from Late Latin mandibula "jaw," from Latin mandere "to chew," from PIE root *mendh- "to chew" (cognates: Greek mastax "the mouth, that with which one chews; morsel, that which is chewed," masasthai "to chew," mastikhan "to gnash the teeth"). Of insect mouth parts from 1826.