(n.) The state of being pensive; serious thoughtfulness; seriousness.

absorption abstraction brown study castle-building close study concentration contemplativeness daydreaming deep thought dreamery dreamfulness dreaminess dreaming dreamlikeness engrossment fantasying gentle melancholy melancholia melancholiness melancholy musefulness musing pipe-dreaming preoccupation profound thought reflectiveness reverie romantic melancholy speculativeness study thoughtfulness tristfulness wistfulness