n (nautical|dated) Any member of a ship's crew who is not required to keep the night-watchOED 2nd edition 1989
n A mechanical device such as a pulley or wheel that does not transmit power, but supports a moving belt etc.http://www.merriam-webster.com/dictionary/idler%20wheelhttp://www.merriam-webster.com/dictionary/idler+pulleyOED 2nd edition 1989