adj. 25B6; adjective
a thoughtful expression : PENSIVE, reflective, contemplative, musing, meditative, introspective, philosophical, ruminative, absorbed, engrossed, rapt, preoccupied, deep/lost in thought, in a brown study, brooding; formal cogitative.
how very thoughtful of you! : CONSIDERATE, caring, attentive, understanding, sympathetic, solicitous, concerned, helpful, friendly, obliging, accommodating, neighbourly, unselfish, kind, compassionate, charitable.
vacant, inconsiderate.