1770, used by Capt. Cook and botanist Joseph Banks, supposedly an aborigine word from northeast Queensland, Australia, usually said to be unknown now in any native language. However, according to Australian linguist R.M.W. Dixon ("The Languages of Australia," Cambridge, 1980), the word probably is from Guugu Yimidhirr (Endeavour River-area Aborigine language)
/gaNurru/ "large black kangaroo."
"In 1898 the pioneer ethnologist W.E. Roth wrote a letter to the Australasian pointing out that gang-oo-roo did mean 'kangaroo' in Guugu Yimidhirr, but this newspaper correspondence went unnoticed by lexicographers. Finally the observations of Cook and Roth were confirmed when in 1972 the anthropologist John Haviland began intensive study of Guugu Yimidhirr and again recorded /gaNurru/." [Dixon]
Kangaroo court is Amer.Eng., first recorded 1853 in a Texas context (also
mustang court), from notion of proceeding by leaps.
[kang-guh-roo] 
) -roo.