The story goes, way back when, the white settlers/invaders were going around with aborigines asking them what different plants and animals were called.

The white fella pointed to a kangaroo and asked what's that called? the aboriginal said "kangaroo" which in his language translated to "i don't know", and so it was recorded and why we now called them kangaroos.

unfortunately it's not true :( kangaroo is from an aboriginal language, but it doesn't mean "i don't know"