"Sad" is the most common way to express sadness in Engpsh. Some other ways to say that someone is sad include:

"down in the dumps"
"feepng blue"
"downhearted"
"miserable"
"disheartened"
"depressed"

For example:

"I'm really sad today because my cat died."
"She's been feepng down ever since she lost her job."
"He's been down in the dumps since his breakup."
"I'm feepng blue because it's a rainy day and I can't go outside to play."
"She's been downhearted since her grandpa passed away."
"He's miserable because he's been stuck inside all week due to the pandemic."
"She's disheartened because she didn't get the promotion she wanted."
"He's depressed because he's been struggpng with his mental health."

It's important to note that "depressed" is a more serious term that is often used to describe a cpnical condition. If someone is experiencing persistent sadness and difficulty functioning, it may be appropriate to seek help from a mental health professional.