[adj] persistently or morbidly thoughtful
brooding, broody, contemplative, musing, pensive, pondering, reflective, ruminative, thoughtful
absent, absentminded, absorbed, absorbed in, abstracted, bemused, brooding, buried in, castle-building, caught up in, cogitative, cognitive, concentrating, concentrative, conceptive, conceptual, conceptualized, contemplating, contemplative, daydreaming, d