Some of Poe's vocabulary is kind of ancient. However, they make his poems much more vivid and alive. Here is some help with his more unusual vocabulary.
ague - fever, chills, associated with malaria
avaunt -- hence, away
Chaldee -- an Armaic dialect that is believed to be the original language used for some parts of the Bible.
chimera - a monster from Greek mythology, a grotesque monster
conflagration - a large, destructive fire
corrobative - to strengthen or support
debauch - uncontrolled or unrestrained drinking, indulgence
diminutive - inidicating familiarity or affection
dirge -- a dirge is a funeral hymn.
dross - worthless or ordinary
Eld -- old times
Eldorado -- a city in South America that led 16th century explorers to go on long journeys into South America in belief that Eldorado would have riches and gold. However, no explorer has ever found this "Eldorado".
evinced - to manifest or demonstrate
felicity - immense happiness
fetters - a chain or shackles for the feet
fidelity - faithfulness
Gethsemane -- this can be referred to as the garden outside of Jerusalem where Jesus was arrested, or a place of spiritual or mental suffering.
gimlet - a tool used for boring holes
Gordian knot -- if I remember correctly, there was a knot in the little town of Gordium (I think it was in Asia Minor) that had a prophecy that the person who undid the knot would become ruler of the world. Alexander the Great supposedly undid the knot, but some historians think he just slashed it in half with his sword, hence the line about the sabre.
gossamer - light, delicate, flimsy
infamy - evil reputation
miasma - poisonous or toxic atmosphere
nepenthe -- an old drug used to remedy grief or sorrow.
odious - causing dislike, displeasure
paean -- a joyous exultant song or hymn
Pallas -- the bust of Pallas refers to the Greek goddess Athena. Athena was the goddess of wisdom. She was sometimes called Pallas Athena .
phantasmagoric - fantastic imagery, dreams
Plutionian -- this could be literally interpretted as something from Pluto. However, I believe Poe meant infernal.
prolixity - excessive in length, tedious wordiness
quaff -- to drink heartily, or a hearty draught, depending on whether it is used as a a noun or verb.
reliquary -- a relic or storage container for religious relics
requiem -- a dirge or solemn chant
scintillating -- to throw off sparks, twinkle
sepulchre -- a tomb
Seraphim or seraphs -- I think this was the plural form of seraphs, which are either an order of angels or celestial beings with three pairs of wings.
paltry - trivial or without importance
rill - a brook
sagacious - showing or possessing farsightedness, good judgment
tarn - a small lake
trepidation - alarm or dread
