from the GNU version of the Collaborative International Dictionary of English
- intransitive v. a sailor's name for the stormy tract of ocean between 40° and 50° north latitude.
- The middle latitudes of the southern hemisphere. So called from the boisterous and prevailing westerly winds, which are especially strong in the South Indian Ocean up to 50° S.
Sorry, no etymologies found.
How exhilarating it must have been to sail the horse latitudes and the roaring forties around the cape, through the icebound gateway between the two greatest oceans of the world.