region or island at northernmost part of the world, Old English, from Latin, from Greek Thyle "land six days' sail north of Britain" (Strabo, quoting a lost portion of a work by Polybius, itself based on a lost account of a voyage to the north by 4c. B.C.E. geographer Pytheas). The identity of the place and the source of the name have sparked much speculation; Polybius doubted the whole thing, and since Roman times the name has been used in a transferred sense of "extreme limits of travel" (Ultima Thule).The name was given to a trading post in Greenland in 1910, site of a U.S. air base in World War II.