One of many interesting facts about words we learned in "The Meaning of Everything: The Story of the Oxford English Dictionary" by Simon Winchester (2003) is that the most complex word in the language is "set."
This "immense" three-letter word has some 430 senses, requiring a 60,000-word definition spread over 24 pages in the tiny print of the published dictionary or 221 pages in PDF form.
Even for the OED, a dictionary that gives comprehensive definitions and examples for every "core" word in the English language, this is an insanely long definition.
So what does "set" mean? Here's the full definition, courtesy of Oxford University Press: