Rack, v. i. [imp. & p. p. Racked (răkt); p. pr. & vb. n. Racking.] [See Rack that which stretches, or Rock, v.] To amble fast, causing a rocking or swaying motion of the body; to pace; -- said of a horse. Fuller.
[1913 Webster]
Racking, n. (Naut.) Spun yarn used in racking ropes.