One of the things I often do as I'm reading a novel or short story is keep track of words whose definitions I do not know or that I find interesting. Either way, these interesting words are ones I feel might be of use in my own writing. That, and it's good to expand one's vocabulary every once in a while.
Read my review of The Alchemist's Pursuit.
altruistic: showing unselfish concern for the welfare of others
aquiline: curved down like an eagle's beak
ascetic: practices self denial as spiritual discipline
avaricious: immoderately desirous of acquiring e.g. wealth
condottiere: A military adventurer of the fourteenth and fifteenth centuries, who sold his services, and those of his followers, to any party in any contest.
connivance: tacit approval of someone's wrongdoing
damask: a fabric of linen or cotton or silk or wool with a reversible pattern woven into it
demimonde: a class of woman not considered respectable because of indiscreet or promiscuous behavior
dyspepsia: a disorder of digestive function characterized by discomfort or heartburn or nausea
ephemeris: an annual publication containing astronomical tables that give the positions of the celestial bodies throughout the year
escritoire: a desk used for writing
fatuity: a ludicrous folly
gematria: a cabbalistic system of interpretation of the Scriptures by substituting for a particular word another word whose letters give the same numerical sum
harridan: a scolding (even vicious) old woman
hematemesis: vomiting blood
insouciant: marked by blithe unconcern
isopsephy: the Greek word for the practice of adding up the number values of the letters in a word to form a single number
licentious: lacking moral discipline; especially sexually unrestrained
malmsey: sweet Madeira wine
miniver: trimming on ceremonial robes consisting of white or light gray fur
miter: a liturgical headdress worn by bishops on formal occasions
niggardly: petty in giving or spending
patriciate: The patrician class; the aristocracy; also, the office of patriarch.
perfidy: betrayal of a trust
plinth: an architectural support or base (as for a column or statue)
sausage stands: I know what a sausage stand is, but thought it interesting that Renaissance Venice had them (or at least Duncan's rendition did).
scuttle: container for coal; shaped to permit pouring the coal onto the fire
sortilege: The act or practice of drawing lots; divination by drawing lots.
succinct: briefly giving the gist of something
tonsure: the shaved crown of a monk's or priest's head