noun
vestigial organ; rudimentary organ
A biological term for an organ that has lost most or all of its original function through evolution.
ヒトの尾骨は痕跡器官の一例だ。
The human coccyx is an example of a vestigial organ.
Compound of 痕跡 (konseki, 'trace, vestige') and 器官 (kikan, 'organ').