sad adjective definition in Unhappiness topic from the Oxford Advanced Learner's Dictionary

sad

 adjective: Unhappiness topic
unhappy or showing unhappiness sad (to do something) We are very sad to hear that you are leaving. sad (that…) I was sad that she had to go. sad (about something) I felt terribly sad about it. She looked sad and tired. He gave a slight, sad smile. The divorce left him sadder and wiser (= having learned from the unpleasant experience).