Full Definition of ANCHOR. 1. : a device usually of metal attached to a ship or boat by a cable and cast overboard to hold it in a particular place by means of a fluke that digs into the bottom.2. : a reliable or principal support: mainstay.efinition of ANCHOR for Kids. 1. : a heavy device attached to a ship by a cable or chain and used to hold the ship in place when thrown overboard.