Epigone: Less-talented follower. "Wittgenstein's epigones had all his puzzlement and none of his insight." For years, my inner ear mispronounced it as e-PIG-onie; it's EPI-gon.

Ophicleide: The keyed brass instrument from which the tuba evolved.

Widdershins: Backwards; counterclockwise; in the wrong or opposite direction.

Tatterdemalion: An increasingly common type of fashion-conscious person who believes that a filthy ragged mess is the new stylish. 

Autochthonous ('Aut-OCHKHK!-thun-us'): One of those rare English words that really makes you clear your throat: if you don't shower everyone with spit between the second and third syllable, you aren't pronouncing it right. I like the anecdote about a teacher who uses the word 'indigenous' in a class, and then turns to one of his (he thinks) dimmer students: "But I don't suppose you even know what 'indigenous' means, do you Mr. Jones?" Mr. Jones replies: "Indigenous? It means autochthonous, doesn't it?" Indeed it does: literally, from the same place. 

Googolplex: 10 to the power of 10 to the power of 100, or 10 to the power of a googol. As I think Carl Sagan pointed out, it would be inconvenient to write out this number in ordinary notation, because the stack of paper coming out of your printer would not fit into the observable universe.

Sinistrodextral: Moving from left to right.

Barycentre: The center of gravity of a multi-body system. The Earth-moon Barycentre is closer to the Earth than to the Moon; the Sun-Earth Barycentre is inside the Sun.

Raddled: stained red. Thomas Hardy's great character Diggory Venn in The Return of the Native was a "reddleman": he sold reddle, or dye, to farmers for marking their sheep. The scene in which he gambles with Wildeve on Egdon Heath at night, the dice on the flat stone made visible only by the light of thirteen glow-worms, was one that convinced me fiction is magic.

Frumious: a state of extreme irritation that makes a Bandersnatch potentially dangerous. From Lewis Carrol's Jabberwocky.

Paleoichthyolarchy: A system of government run by extinct fish. OK, I made this one up. Some non-existent words are just aching to be invented, and that's what makes us writers get up in the morning. Even poltroons like me.

Poltroon: Someone who likes to stay up late and get up late, despite all the sneering of people who sleep the same number of hours only earlier. Favorite famous poltroon: the French philosopher and mathematician René Descartes. A great prose stylist, he was also one of the driest wits in the western canon, and revolutionized western philosophy while lying in bed all morning.

Eleemosynary: Of or supported by charity.

Deliquescence: Melting away by absorbing moisture from somewhere else - as when you put salt on ice.

Streptomycin: The antibiotic, C21H39N7O12. It was discovered in the United States near the end of World War II. Because of his publisher's connections, George Orwell, who was suffering from tuberculosis, was one of the first people in the UK to take it. Unfortunately he was allergic to it, and it could not save him; he died of TB in January 1950 at the age of 46.

Bodhisattva: An enlightened being who has delayed his or her own attainment of nirvana to help others.

Loxodrome: (1) the path across the globe made by a vessel maintaining a constant compass bearing; (2) the place where you take off and land in a smoked salmon.

Euphuism: I love this word because of how I learned it. I once found myself teaching English to a Dutch businessman whose English was already idiomatic, elegant, and exact. I tried to stretch him by asking him to define difficult words, such as euphemism. "Ah yes," he said. "Not to be confused with euphuism, which as we all know is an elaborate sixteenth century prose style." To be taught your own language by a foreigner is a humbling thing.

Boustrophedon: A poem written by an ox. Well, no, but get this for obscure: a poem written with the lines going L-R then R-L then L-R, as in furrows ploughed by an ox.

Amygdaline: Almond-shaped.

Turbid / tumid / turgid / torpid: Muddy / swollen / bloated or overly complex / sleepy.

D'Arvit: A fairy swear word that's too rude to translate. From Eoin Colfer's wonderful Artemis Fowl books. It has become the cuss of choice in our house.

Bowdlerise: To take a book or other text and edit out all the rude or depressing bits, and/or tack on a happier ending. The word is from Thomas Bowdler, who in 1818 published a 'family' edition of Shakespeare. He is often considered a ridiculous figure, but I understand that he never did write in new material, merely deleting offensive words and phrases, and his edition probably resulted in many more children getting to read Shakespeare.