The term 'GNU' is a recursive acronym for 'GNU's Not Unix, ' and is used to refer to the open source operating system of the same name. The first crossword solution, 'WILDEBEEST, ' is a large African ANTELOPE with long curved horns. The second solution, 'ANTELOPE, ' is a type of even-toed ungulate native to Africa and Eurasia. The third solution, 'Africanantelope, ' is a more specific term for antelopes found in Africa. Finally, the fourth solution, 'crosswordstaple, ' is a term used to describe words that are commonly used in crosswords.