"The Ice-Demon" by Clark Ashton Smith

A fathom is 6 feet (1.8288 meters). Well, 6 feet for the US, in the UK it's more complicated and could vary from 5 to 7 feet. The word is typically used in measuring the depth of water.

effulgent: shining brightly; radiant

panoply: in this context, a complete set of arms and armor. More generally, a complete or impressive collection of things.

gelid: icy; extremely cold

glaucous: of a dull greyish-green or blue color

serried: standing close together

The use of the word 'pendant' in this story is curious. Obviously we're not referring to jewelry. It is perhaps best to just go directly to the word's etymology from the Middle English: denoting an architectural decoration projecting downwards, or the Old French pendre, meaning 'hanging'. We understand this meaning when the word is first used in this story as an adjective: pendant icicles. Afterwards, the word is used in a way where the 'icicles' is left implied, we just supposed to remember it.

buskin: A calf-high or knee-high boot of cloth or leather

bouleversement: an inversion, especially a violent one

parhelia: plural of parhelion, a bright spot in the sky appearing on either side of the sun, formed by refraction of sunlight through ice crystals high in the atmosphere

atavistic: relating to or characterized by reversion to something ancient or ancestral

legerdemain: skillful use of one's hands when performing conjuring tricks; or more generally: deception or trickery

purlieu: the area near or surrounding a place

thew: muscles and tendons perceived as generating physical strength

propitiate: win or retain the favor of a god or spirit by doing something that pleases them

This story might make for a pretty good movie. Of course, you can't trust Hollywood with it, they will add in some female love interest that makes no sense whatever, so it would have to be done by some indie group. But if a faithful adaptation were made, and there's still quite a bit of room for artistic license even while remaining highly faithful to the source, it could be pretty intense.

To follow along: http://www.eldritchdark.com/writings/short-stories/96/the-ice-demon

So the stories are arranged in in-world chronological order. We saw in "The White Sybil" that this glaciation was prophesied long before it ever happened. Then we saw in "The Coming of the White Worm" that Rlim-Shaikorth brought forth with him glaciation everywhere he went. But we are told in this story that the glaciers here are from Polarion. This leads us to many questions: was the glaciation of the White Worm related in any way to the glaciers of Polarion? If not, did the White Worm's glaciers melt before these Polarion glaciers advanced? Or did the White Worm's glaciers make it possible for the Polarion glaciers to begin advancing southward? Did the White Worm's glaciers merge with the Polarion glaciers? Are the people in-world confusing the glaciers of the White Worm for the glaciers from Polarion? Are the White Worm's glaciers in fact the prophesied glaciers from Polarion? I need to know!! Unfortunately, I suspect these questions were never answered by Smith, so we'll never know :(