WHAT DOES CUAN SLOT MEAN?

TS Eliot attracts from this myth during the Dry Salvages: "And also the ragged rock while in the restless waters,/Waves clean over it, fogs conceal it;/On a halcyon day it truly is merely a monument,/In navigable weather it is usually a seamark/To lay a training course by: but during the sombre season/Or the sudden fury, is exactly what it generall