Being sad is a common emotion that we all experience at some point in our lives. It could be due to a number of reasons such as loss, disappointment, or loneliness. When we are sad, we tend to withdraw from others and seek comfort from within ourselves. There are several synonyms for the word "be sad", and you can use them to express your emotions in a more nuanced way. Some of these synonyms include feeling blue, downhearted, unhappy, despondent, and gloomy. Each of these synonyms has its own connotation, so choose the one that best describes your particular feeling of sadness.