What part of speech is signal?

"Signal" can be several parts of speech depending on how it's used in a sentence:

* Noun: A sign or indication.

* Example: "The smoke was a signal of a fire."

* Verb: To give a signal.

* Example: "The referee signaled for a timeout."

* Adjective: Relating to or used for signaling.

* Example: "They used signal flares to call for help."

Let me know if you want examples of how "signal" is used in a particular part of speech.