Why are reveries sometimes called “brown” studies?

Question

Though this idiom is by no means very common, one comes across it now and then. (I just came across it again today, which is why I'm asking this question.)

Why is a "brown study" so named?

Answer 1

From TheFreeDictionary.com:

brown study n a mood of deep absorption or thoughtfulness; reverie ...
Gloomy meditation or melancholy is known as being in a brown study.

This is a somewhat archaic usage (it may be a rural or Southern U.S. regionalism, but I don't have access to my tools for tracking that down just at the moment), although it has been used in poetry to good effect. Consider this stanza from John Crowe Ransom's "Bells for John Whiteside's Daughter":

There was such speed in her little body,
And such lightness in her footfall,
It is no wonder her brown study astonishes us all

He's talking about death as a "brown study" in an example of understatement.

Edit

@Kit brings up a good point. "Brown" used to mean gloomy exclusively. From Etymonline:

brown O.E. brun "dark, dusky," only developing a definite color sense 13c

Answer 2

According to the Phrase Finder, brown study is very old usage of "brown" to indicate a gloomy mood and "study" in the sense of deep thought. More modernly, we would probably more immediately grasp "black mood," since black is the new brown, as it were.

Answer 3

Slightly surprisingly, since neither of its words now seems to fit the meaning, brown study was originally a tautology and pleonasm.

The OED first cites it from 1552^*. As other answers note, brown at this date could mean dusky, dark more generally than today, and hence figuratively gloomy, serious. But besides that, study also had a slew of now-obsolete meanings, including a state of mental perplexity or anxious thought and a state of reverie or abstraction, with uses like:

He was in suche a study he herd not what Gouernayle said.
      —Malory, Morte d'Arthur, 1470–85

I was at first in a study what to do, at last I promised.
      —R. Meeke, Diary, 1689

So a brown study then was closely analogous to the not-yet-so-opaque a blue funk. To be in a study was bad already; a brown study really served to emphasise the gloom.

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^{* in the rather extraordinary-sounding Manifest Detection Diceplay, which turns out upon googling to be a pamphlet on cheating at cards, A Manifest Detection of the Most Vyle and Detestable Form of Diceplay, by one Gilbert White.}

Answer 4

The closest meaning today of 'brown study' is 'brooding'. As used into the mid-20th century, didn't just mean a melancholy mood or 'reverie' and it didn't mean 'depressed' in our usual sense. It meant thinking so deeply about something troubling that one becomes wrapped up in it and temporarily cut off from other people or asocial. In essence, if one is in a brown study, one is 'studying' (thinking hard about) something in a 'brown' or darkly shadowed mood.The assumption was, though, that people going into brown studies occasionally and then come out of them.