Deeply or seriously thoughtful
Brooding
Broody
Contemplative
Meditative
Pensive
Pondering
Reflective
Ruminative
Thoughtful
A calm, lengthy, intent consideration
Contemplation
Reflection
Reflexion
Rumination
Thoughtfulness
Consideration
Introspection
Meditation
Retrospect
Self-contemplation
Self-examination
Speculation
Study
Cogitation
Muse