What does "brown study" mean?

A melancholy mood accompanied by deep thought; a moody daydream.

Brown study

Common synonyms include: absence of mind, absentmindedness, absorption, abstractedness, abstraction, bad dream.

noun

noun ·Rare ·Advanced level

Noun

1
A melancholy mood accompanied by deep thought; a moody daydream. dated, idiomatic
"Phædra. [...] Why Soſia! What, in a brown Study? / Soſia. A little cogitabund, or ſo; concerning this diſmal Revolution in our Family!"
2
a state of deep absorption or thoughtfulness wordnet

"Phædra. [...] Why Soſia! What, in a brown Study? / Soſia. A little cogitabund, or ſo; concerning this diſmal Revolution in our Family!"

From obsolete brown (“gloomy”) and study.