Merriam-Webster's Word of the Day for May 10, 2012 is:

tranche • \TRAHNSH\  • noun
: a division or portion of a pool or whole

Examples:
"The funds are doled out in tranches over time…." — From an article in The Economist, March 10, 2012

"The 1917 law … allowed $8 billion in national debt, the first tranche of an ultimate $30 billion debt to fund World War I, repayable in gold." — From an article by David Malpass in Forbes, February 27, 2012

Did you know?
In French, "tranche" means "slice." Cutting deeper into the word's etymology, we find the Old French word "trancer," meaning "to cut." The word emerged in the English language in the late 19th century to describe financial appropriations. Today, it is often used specifically of an issue of bonds that is differentiated from other issues by such factors as maturity or rate of return. Another use of the French word "tranche" is in the French phrase "une tranche de vie," meaning "a cross section of life." That phrase was coined by the dramatist Jean Jullien (1854-1919), who advocated naturalism in the theater.