I think 'intelligence' represents how slippery all concepts are. Think about the definition of intelligence. According to the most common scientific definition, it's basically the ability to see patterns. The funny thing about that is that the ability to see patterns is basically what makes someone a good scientist, so scientists have defined 'intelligence' to mean having the potential to be good at science. Similarly, if you look at the CIA, intelligence means having information about enemy countries, because that's what makes a good CIA officer. If you were to ask a painter about the definition of intelligence, they'd probably tell you that it has something to do with being good at painting.
All words are defined by the types of people who are most likely to spend time thinking about the definition of that word, which means that essentially every concept in the every language is fundamentally biased by the worldview of the sort of person who would spend time thinking about that concept. And since science, logic, and knowledge are fundamentally based on these concepts in terms of looking for what to talk about and measure, I think this may be a serious epistemological problem that leaves humans capped at a certain level in terms of what we can know.
This is also why I'm generally skeptical of sites like Less Wrong, as I think the real limits of rationality and human knowledge have almost nothing to do with the 'official' list of logical fallacies that these sites tend to focus on.
I took Latin in high school because I liked etymology (and because greek letters were really too weird):
From Latin intellegentia ("the act of choosing between, intelligence"), from intellegō ("understand"), from inter ("between") + legō ("choose, pick out, read"). [taken from wiktionnary]
So intelligence is the ability to understand, that's all (the etymologic link with dichotomy is beautiful).
Now how we understand (and please don't confuse yourself again with "oh yeah but what does 'understand' really mean") is the hard part.