Today's word is litotes, a word I cannot remember ever reading before. Off, because the meaning of the term is something we do every day. Well, I do. It means, according to the Wikipedia, "a figure of speech in which understatement is employed for rhetorical effect when an idea is expressed by a denial of its opposite . . ." For example, "not as young as he was", meaning "old". It is common in English and many other cultures.
An interesting search, too - try it. The search for litotes returns almost entirely definitions rather than uses of the word in a practical context - in other words, people seem to define the word more than use it. They use the concept (double negatives for emphasis, or ironical emphasis) frequently. So about.com quotes Queen Victoria's "We are not amused" as a litotes, and has a useful entry with lots more quotes. Wiktionary points out that it is an anagram of toilets, but not if you use the Greek spelling of λιτότης
The Alpha Dictionary reads one pronounciation of it to you and provides the valuable information that the singular and plural have the same form. The SIL site has examples from the Bible (John 6:37) and Eduard Schevardnadze, and proper references. The SIL is or was the Summer Institute of Linguistics. Even Facebook has a page on litotes although, alas, it is taken from the Wikipedia. It does add the information that 111 people like the word. One of them is me.