: feeling or showing sorrow or unhappiness <I'm sad that you're leaving.><The dog had sad eyes.>
: causing sorrow or unhappiness <sad news>
Word History of SAD
The word sad goes far back into the past of the English language, though modern meanings such as “unhappy” or “causing sorrow” give us little idea of its history. It comes from the Old English word sæd, which meant “full, having had enough,” a sense matched by related words in other languages, such as German satt. In Middle English, sad continued to mean “full,” but it also developed many other senses, such as “firmly established, fixed,”“solid, weighty,”“sober, serious,”“true, real,” and “deep, intense (of a color).” The meaning “sorrowful” was in use fairly early, by about 1300, though strangely enough only this sense among all the others has lasted into modern English.