dreamily thoughtful; thoughtful with a hint of sadness; contemplative
Seeing her pensive expression, he asked her, "Is something troubling you?"
pensare (to weigh, consider) (Latin)
With a pen in your mouth, you are always indulged in somekind of thought. PENSIVE=PEN+SAVE. with a PEN in your mouth you are dreaming about your SAVIngs (SIVE) pensieve is a word in harry potter which is collection of thoughts. so it is like indulging in thoughts.