Here are some possibilities:
* Noun: When referring to a system of communication used by humans.
* Example: "English is a complex language."
* Adjective: When describing something as relating to language.
* Example: "She has strong language skills."
* Verb: When referring to the act of expressing oneself.
* Example: "They language their needs to the manager."
The part of speech depends entirely on the context of the sentence.