Oxford University Press publishes a reference book entitled Better Wordpower -- a terrific reference of vocabulary from different professions and disciplines almost guaranteed to make you sound like an expert. This is good enough, but inside you'll also find a synonym / antonym list, common foreign phrases, words that are often confused, a wonderful section discussing basic etymology (really good for aspiring GRE test takers), and a collection of difficult words.

The difficult words are less common, more provocative, than many of the GRE words I had the pleasure of studying a couple of years ago. The GRE words can consider themselves replaced. Oxford's list piques both interest and curiosity. Musical, Updike words.  

Try building a sentence around these suckers. It’s not so easy. These words have to be fitted to a paragraph, tailored to a character’s voice or scene, or they’ll sound like you’re trying too hard.  Too writerly.

From the Oxford book:

• piceous  - Black, glossy, like pitch. I’m using this and I know exactly where. It’s perfect.
• verglas - A thin coating of ice or frozen rain (on an exposed surface). The word sounds fragile.
• deipnosophist - a master of the art of dining, according to Oxford; a master at the art of table conversation, say other sources. Sitting next to someone you can't stand at dinner, especially if you're on a diet, makes you a diepnonosophist.
• claque - A group of people hired to clap in a theater. What does it pay?
• serein - a fine rain falling in tropical climates from a cloudless sky after sunset. You get the same thing outdoors at New York restaurants in the dead of summer humidity, but here they just call it "plumbing." (The Old French word is serain, meaning dusk.) 
• pavonine - Like a peacock. Fifties hair?
• limaceous - Related to slugs or snails. Lots of possibilities.
• virago - A fierce or abusive woman. Not quite the same as the maiden goddess of the harvest.
• callipygian - Having a beautiful, well-shaped butt. "Her callipygian days were behind her." 

Your assignment is to construct sample sentences. Let's post a few!