noun · fine dust or powder produced by chalk, often from writing on a blackboard

黑板擦一拍，教室里到处都是白粉。

adjective · cosmetic powder applied to the face for makeup or skin whitening

她在脸上涂了一层薄薄的白粉。

noun · a colloquial slang term for the illegal narcotic drug heroin

他因为贩卖白粉被警方逮捕了。