There are around a half-million words in the full Oxford English Dictionary, though most people use only a few thousand in everyday communication. Randall Munroe of xkcd explains the Saturn V rocket using only the 1,000 most commonly-used English words. This comic grew out of Munroe's journeys into Simple English Wikipedia. You can see another example here. If you want a taste of how difficult it is to explain things using only the thousand most common words, The Up Goer Five Text Editor will point out any words you use that are too uncommon. However, if you are going to explain something to children or people who are learning English as a second language, the simpler the better. Link -via Metafilter