n (US) A region of land within which water flows down into a specified body, such as a river, lake, sea, or ocean; a drainage basin.
n A criticalpoint marking a change in course or development.
n (Canada|British) The time after which material of more adult nature (violence, swear words, sex) may be broadcast on television or radio, either one laid down or one contrived (e.g. when children are not watching...)