sad (Adjective) — Experiencing or showing sorrow or unhappiness. ex. "feeling sad because his dog had died" ex. "Better by far that you should forget and smile / Than that you should remember and be sad"
sad (Adjective) — Of things that make you feel sad. ex. "sad news" ex. "she doesn't like sad movies" ex. "it was a very sad story" ex. "When I am dead, my dearest, / Sing no sad songs for me"
sad (Adjective) — Bad; unfortunate. ex. "her clothes were in sad shape"
sad (Adjective) — (spoken slang) unfashionable and boring.
sad (Noun) — A form of depression caused by the lack of natural light during the winter months.