At one level, few things are simpler than a dictionary: a list of the words people use or have used, with an explanation of what those words mean, or have meant. At the level that matters, though – the level that lexicographers fret and obsess about – few things could be more complex. Who used those words, where and when? How do you know? Which words do you include, and on what basis? How do you tease apart this sense from that? And what is “English” anyway?