One of the most repeated word stories in English is false. Kangaroo does not mean "I don't understand."
The legend goes like this. Captain James Cook's men pointed at a strange hopping animal and asked what it was called. A local man answered "kangaroo," meaning he did not understand the question, and the sailors took that as the name. It is a neat joke about colonial misunderstanding. It is not what happened.
The real story starts in 1770. Cook's ship, the Endeavour, was being repaired at the Endeavour River, where Cooktown in Queensland stands today. While they waited, the crew recorded words from the local people, who spoke Guugu Yimithirr. It became the first Aboriginal Australian language to be written down.
One of those words was the name of the animal. Cook's journal for August 1770 names "the Kangooroo or Kanguru, so called by the Natives," according to Wordorigins.org. Joseph Banks, the expedition's botanist, recorded the same word.
So where did the myth come from? Part of the answer is geography. Australia had hundreds of languages, each with its own names for the animal. Watkin Tench, a British officer, wrote in 1793 that the people he knew called it "pat-ag-a-ràn," and that kangaroo had been introduced by Europeans. Doubts like his let the story grow that the word was not really Aboriginal at all.
The explorer Phillip Parker King added to the confusion. He visited the Endeavour River in 1819 and 1820 and was told the local word was menuah, perhaps for a different animal.
Linguistics settled it. Etymonline says research by John Haviland confirmed in 1972 that Guugu Yimithirr has the word gangurru. It did not mean every kangaroo. It named one particular kind, a large black or grey kangaroo. English stretched it to cover the whole family.
The word has kept hopping. "Kangaroo court," for a sham trial, is first recorded in 1850 in the American Southwest, probably from the idea of proceeding by leaps. Australians shortened the animal to "roo" by 1904.