The denotation of connotation is the suggestive meaning of a word, and all of the cultural associations it brings up.
Two words can mean exactly the same thing and have wildly different connotations. For example, if you call someone economical, it's a polite, positive way of saying they're smart with money. If you call them cheap or stingy, well that's just plain rude.
It goes the other way, too. One word can have different connotations, depending on the context and cultural experiences of the person writing it or the person reading it. For some people, the word intellectual refers to a smart person, and that's a good thing, right? But for others, intellectual can connote elitism, snobbishness, and all sorts of other not-so-good things.
Think of connotation as the murky haze hanging around the literal meaning of a word. Trying to figure out connotations of words can be one of the most confusing and rewarding aspects of reading literature.