Here are some examples of how it's used as an adjective:
* "The building has secure doors."
* "She felt secure in her job."
However, "secure" can also be used as a verb, meaning to make something safe or to obtain something. For example:
* "The police secured the crime scene."
* "The team secured a victory."
Therefore, "secure" is not a noun; it is an adjective or a verb, depending on the context.