According to my dictionary, quiet can be used as an adjective, a noun or a verb.
What part of speech is quiet in the imperative "Quiet, please!"?
I need native speakers' help.
It depends on what you consider the unspoken part of the sentence to be. If it is to be read as "Be quiet, please", then "quiet" is an adjective. If it is to be read as "Can we please have some quiet in here!", then "quiet" is a noun.
Your post specifically identifies the sentence as using the imperative, in which case it's an adjective. "Be" is unspoken.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.