* Adjective: Describing a state or quality, like "The library was very quiet."
* Noun: Describing a state of stillness, like "We enjoyed the quiet of the countryside."
* Interjection: Used to request silence, like "Quiet! I'm trying to concentrate."
* Verb: Used to make something silent, like "Please quiet the children."
So, without context, it's impossible to say for certain which part of speech "quiet" is.