n. [ OE. gerfaucon, OF. gerfaucon, LL. gyrofalco, perh. fr. L. gyrus circle + falco falcon, and named from its circling flight; or cf. E. gier-eagle. See Gyre, n., Falcon. ] (Zool.) One of several species and varieties of large Arctic falcons, esp. Falco rusticolus and the white species Falco Islandicus, both of which are circumpolar. The black and the gray are varieties of the former. See Illust. of Accipiter. [ Written also gerfalcon, gierfalcon, and jerfalcon. ] [ 1913 Webster ]