The term 'CAPTAIN's Post' refers to the position of the CAPTAIN on a ship. The CAPTAIN is responsible for the overall operation of the vessel, including navigation, crew management, and safety. The CAPTAIN is usually stationed at the HELM, which is the four-letter word used in the crossword solution. The HELM is the wheel or tiller that controls the direction of the ship. The CAPTAIN is in charge of steering the ship and making sure it reaches its destination safely.