-- http://www.macobserver.com/tip/2007/08/08.1.shtml -- http://www.macobserver.com/tmo/article/Thesaurus_Mac_OS_X_Style/

Word Autocompletion

Whenever you are typing anywhere in Mac OS X, you can simply press the Esc key while typing any word and you’ll be presented with a menu of all the words and phrases that begin with those letters and you can choose any of them. In the example shown here, I’d entered ‘appl’ before hitting the Esc key. Though not very useful in regular usage, it does help when you remember the first few letters of a word but aren’t sure how it ends.