It's a simple, standalone word.
However, you can find related words with prefixes and suffixes, like:
* Prefixes:
* Un-sad: (meaning not sad)
* Over-sad: (meaning excessively sad)
* Suffixes:
* Sadness: (the state of being sad)
* Sadly: (in a sad manner)
Let me know if you'd like to explore other words with prefixes and suffixes!