If you are thoughtful, you are quiet and serious because you are thinking about something.
Nancy, who had been thoughtful for some time, suddenly spoke.
南希沉思半晌后,突然开口说话了。
If you describe someone as thoughtful, you approve of them because they remember what other people want, need, or feel, and try not to upset them.
a thoughtful and caring man.
一个考虑周到、关心体贴的男人。
If you describe something such as a book, film, or speech as thoughtful, you mean that it is serious and well thought out.
a thoughtful and scholarly book.
一本既有思想深度又有学术价值的书。