The term 'IT'S OPEN AND SHUT' can be solved by the crossword solution 'DOOR', which is a four-letter word. A DOOR is an opening or closing structure used to block off an entrance, typically consisting of an interior side that faces the inside of a space and an exterior side that faces the outside. Doors are usually made of a hard, impermeable, and hard-to-break substance such as wood or metal, but sometimes consist of a hard frame into which glass or screens have been fitted.