pensive

Engaged in, involving, or reflecting deep or serious thought.

He sat in pensive silence, weighing his options carefully.

Having the appearance of deep, often melancholic, thinking.

The author’s tone grows pensive in the final chapters.

Looking thoughtful, especially from sadness.

Abstruse thought and profound researches I prohibit, and will severely punish, by the pensive melancholy which they introduce

Through the deep grass the faces of the three children glowed like pensive moons.