Rack1  —n. 1 framework, usu. With rails, bars, etc., for holding things. 2 cogged or toothed bar or rail engaging with a wheel or pinion etc. 3 hist. Instrument of torture stretching the victim's joints. —v. 1 (of disease or pain) inflict suffering on. 2 hist. Torture (a person) on the rack. 3 place in or on a rack. 4 shake violently. 5 injure by straining.  on the rack suffering acute mental or physical pain. Rack one's brains make a great mental effort.  [low german or dutch]