pensive

1. Deeply, often wistfully or dreamily thoughtful.

2. Suggestive or expressive of melancholy thoughtfulness.

Synonyms: These adjectives mean characterized by or disposed to thought, especially serious or deep thought. Pensive often connotes a wistful, dreamy, or sad quality: "while pensive poets painful vigils keep" (Alexander Pope).
Contemplative implies slow directed consideration, often with conscious intent of achieving better understanding or spiritual or aesthetic enrichment: "The Contemplative Atheist is rare ... And yet they seem to be more than they are" (Francis Bacon).
Reflective suggests careful analytical deliberation, as in reappraising past experience: "Cromwell was of the active, not the reflective temper" (John Morley).
Meditative implies earnest sustained thought: The scholar was reticent, aloof, and meditative.
Thoughtful can refer to absorption in thought or to the habit of reflection and circumspection: Thoughtful voters carefully considered the candidates.