"The Double Shadow" by Clark Ashton Smith

Pharpetron? Is that his name? Pharpetron? What the hell kind of a name is Pharpetron?

Lieutenant Scheisskopf had the facts at his finger tips. "It's Pharpetron's name, sir," he explained.

*eyeroll*

seine: a fishing net which hangs vertically in the water with floats at the top and weights at the bottom edge, the ends being drawn together to encircle the fish

byssus: a fine textile fiber and fabric of flax

empery: empire

dun: a dull grayish-brown color

trove: treasure

volute: a deep-water marine mollusk with a thick spiral shell

ambergris: a solid, waxy, flammable substance of a dull grey or blackish colour produced in the digestive system of sperm whales. It can be used in cooking, in making perfume, incense, for scenting cigarettes, and all kind of purposes.

wrack: in this context, any of a number of coarse brown seaweeds which grow on the shoreline, frequently each kind forming a distinct band in relation to high- and low-water marks.

mordant: a substance that combines with a dye or stain and thereby fixes it in a material

recondite: little known; abstruse

infrangible: unbreakable; inviolable

adumbration: a shadow or faint image of something

purulence: condition of containing or forming pus. Yum!

deliquescent: we have here two choices of definition, neither one of which is an exacting fit, so clearly the author was using the word here more poetically than literally, in which case you chose which definition you think better fits what is going on here: 1) tending to melt or dissolve, especially tending to undergo gradual dissolution and liquefaction by the attraction and absorption of moisture from the air, or 2) having repeated division into branches

Recall the context: and the face and fingers seemed to drip in the moon- light with a deliquescent corruption.

fain: in this context here, probably the best fit is 'gladly'

To follow along: http://www.eldritchdark.com/writings/short-stories/53/the-double-shadow

Not a bad little tale of creeping horror, eh? So now we are left with the question of what is the conjured entity, and to what use it was put by the serpent-men?