What is a suffix for spy?

There isn't a common, widely used suffix specifically for "spy". However, depending on the context, you could consider these options:

For a person who spies:

* -er: spyer (common, but might sound informal)

* -ist: spyist (less common, but more formal)

* -agent: spyagent (common, emphasizes role)

* -master: spymaster (emphasizes experience or leadership)

For the act of spying:

* -ing: spying (common, emphasizes action)

* -age: spyonage (common, emphasizes the practice)

* -craft: spycraft (emphasizes skills and methods)

For a related concept:

* -ware: spyware (software designed for spying)

* -cam: spycam (a hidden camera used for spying)

The best suffix will depend on the specific meaning and context you want to convey.