The term 'EXTREMELY ARID' can be summarized by the crossword solution 'SAHARAN', which is a seven-letter word. The Sahara Desert is the world's largest hot desert, located in North Africa. It is known for its extreme aridity, with temperatures reaching up to 122°F and an average annual rainfall of less than 4 inches. This makes it one of the most arid regions on Earth, and thus an apt description for the term 'EXTREMELY ARID'.