ulna (n.)youdaoicibaDictYouDict[ulna 词源字典]
inner bone of the forearm, 1540s, medical Latin, from Latin ulna "the elbow," also a measure of length, from PIE *el-ina-, extended form of root *el- (1) "elbow, forearm" (see ell (n.1)). Related: Ulnar.[ulna etymology, ulna origin, 英语词源]