brown study

Etymology
From obsolete and.

Noun

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

Usage notes
Usually said as “somebody is in a brown study”.

Translations

 * Chinese:
 * Mandarin: 冥思出神
 * Finnish:
 * French:, ,
 * Russian: глубо́кое разду́мье
 * Spanish: