cercus
Concise Oxford English Dictionary © 2008 Oxford University Press:
cercus /ˈsəːkəs/
▶noun (pl. cerci /-kʌɪ/) Zoology either of a pair of small appendages at the end of the abdomen of some insects and other arthropods.
– origin C19: from mod. L., from Gk kerkos ‘tail’.
'cercus' also found in these Oxford entries:

