Abrosia

Abrosia: This is a strange word because it sounds too much like ambrosia – the name given to the supposed food and drink of the gods or absolutely heavenly food for mortals. But abrosia would be torture for someone expecting ambrosia, because abrosia means fasting or not consuming any food.

Lamprophony

Lamprophony (noun): Clear enunciation

There's no trace of lamps, pros, or phonies in this word's definition.  If you know that -phony means sound, you might guess that lamprophony is the sound of lampreys.  (Do they even make noise?) But no, lamprophony turns out to be a rather boring word that means clear enunciation.  (The Greek root lampro- means clear or distinct.)

Restive

Restive [adjective]: Restless or agitated.

Don't be fooled by the root word rest.  Rather than meaning restful, restive actually means restless. It can also mean disobediently stubborn or recalcitrant. This is a fine example of one of those sneaky words that means the opposite of what you may think it means.

Tortuous

Tortuous [adjective]: Twisting, having sudden or sharp turns and corners.

Because it sounds so much like torturous, most people confuse the two. While something can be torturous, it doesn't also mean that it's tortuous (or vice-versa). For instance, a book with many twists and turns can be tortuous, but quite an exciting and engaging read. A torturous book, on the other hand, is just unpleasant to read.

Fungible

Fungible: adjective: Replaceable of exchangeable for a similar item.

Though not as obscure as other strange English words, fungible looks deceptively like fungus and edible, which might put you in the mind of edible fungi. This word is actually an economic term meaning replaceable or exchangeable for another of its kind.  Currency is a fungible commodity; you can use any $20 bill to pay for a $20 item.

Fagin

Fagin (noun): an adult who instructs and involves others (usually children) in crime.

This is a prime example of a character's name from a novel that became a word. Fagin is a petty criminal in Charles Dickens' "Oliver Twist" who manages and trains a band of thieving young boys.

Eutrapely

Eutrapely (noun): Pleasantness in conversation. This is one of the seven moral virtues that Aristotle enumerated.

Is it a sign of the times, perhaps, that this word is now obsolete whereas there are no shortage of words to describe unpleasant conversation?