the word refers in general to an animal's lair. but in the US after world war 2, it took on another meaning: a study in a house. growing up in suburban connecticut, i learned the word by visiting friend's homes or overhearing them talk. the impression i had was clear: the den was a place for dad, his books, his computer.
i wonder how "study" got to be associated with the word "den." isn't it odd? my theory is this: that the word was created by marketers for suburban housing developers to spice up an old concept. for a more current example, think of the odd (to me) word "breakfast nook." this word did not just come out of nowhere: marketers made it. and some ordinary people actually use it.
but why did marketers use the word "den" and not something else? i guess it had to do with the obsession with gender after world war 2. war and depression and industrialization had rendered old gender categories more and more irrelevant. corporations and citizens after the war found ways to recreate gender lines. even if it was clear that with machines, for example, women could do the exact amount of work as a man, male-dominated society (with the acquiescence of most women) found new ways to prove that women were essentially "different" from men: their "natures" were domestic. they were born to be inside. they were not as rational. etc etc.
so i think the word "den" was a way for marketers to link maleness to a certain special space within the female space of the home. a den is for animals. it was also to be for men looking to retreat to a more primal identity. in the "den" he would not be feminized, but retain his power in splendid isolation. isn't it funny that a place for books, associated with civilization, should be relabelled as savage and animalistic? but savage and primordial in a good way. . .
i wonder if the word is still used by builders or by suburbanites themselves. or was it just a transient usage from the 80s that disappeared later.
am i wrong? i would look in the OED online, but i do not have a subscription.