Synonyms: pensive, contemplative, reflective, meditative, thoughtful
These adjectives mean characterized by or disposed to deep or serious 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: "[He] had envisioned an actual grove of academe through which scholars young and old might take contemplative strolls" (Tom Wolfe).
Reflective suggests careful analytical deliberation, as in reappraising past experience: "She ... is as wise as if she'd been on this earth for eighty years. Her nature is reflective—not all over the map, like mine" (Alice Munro).
Meditative implies earnest sustained thought: "She sat with her shoulders rounded in some clearly deepening meditative privacy and forgot me" (E.L. Doctorow).
Thoughtful can refer to absorption in thought or to the habit of reflection and circumspection: "I had spoken at once ... to Silvius about our departure, and we talked the matter over, for he was a thoughtful and intelligent child, and children have a wisdom of their own" (Ursula K. Le Guin).