gyrfalcon n.

mid-13c., faucon, from Old French faucon "falcon" (12c.), from Late Latin falconem (nominative falco) "falcon" (source also of Old Spanish falcon, Portuguese falcão, Italian falcone, Old High German falcho, German Falke, Dutch valk), probably from Latin falx (genitive falcis) "curved blade, pruning hook, sickle, war-scythe" (see falcate); the bird said to be so called for the shape of its talons, legs, or beak, but also possibly from the shape of its spread wings.

The other theory is that the Latin bird name falx is of Germanic origin and means "gray bird" (from PIE root *pel- (1) "pale"), which is supported by the antiquity of the word in Germanic but opposed by those who point out that falconry by all evidences was imported from the East, and the Germans got it from the Romans, not the other way round.

1560s, "a circular motion," from Latin gyrus "circle, circular course, round, ring," from Greek gyros "a circle, ring," related to gyrós "rounded," perhaps from PIE root *geu- "to bend, curve" (source also of Armenian kor "crooked," Lithuanian gurnas "hip, ankle, bone," Norwegian kaure "a curly lock of hair"). The noun is attested in Middle English only in reference to ship's tackle (early 15c.).