To loosen or remove by turning in a counterclockwise direction. He had to unscrew the lid to open the jar.
To detach or separate by turning in a counterclockwise direction. She unscrewed the light bulb to replace it with a new one.
(intransitive) To become loosened or detached by being turned, typically in a counter-clockwise direction. The cap unscrews easily, so be careful not to spill the contents.