A flying scud, drifting clouds. (Icelandic, rek, drift; verb, recka, to drive.)
The cloud-capped towers, the gorgeous palaces, The solemn temples, the great globe itself, Yea, all which it inherit, shall dissolve And ... leave not a rack behind.
Shakespeare: Tempest, iv. 1.
The instrument of torture so called was a frame in which a man was fastened, and his arms and legs were stretched
till the body was lifted by the tension several inches from the floor. Not unfrequently the limbs were forced thereby out of their sockets. Coke says that the rack was first introduced into the Tower by the Duke of Exeter, constable of the Tower, in 1447, whence it was called the “Duke of Exeter's daughter.”
(Dutch, rak; verb, rakken, to stretch: Danish, rag; Anglo-Saxon, reac.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894