floorboard
A long, flat wooden board that makes up a floor.
A floorboard is one of the long, flat pieces of wood that fit together to make a floor. If you've ever walked across an old wooden floor and heard it creak, you were stepping on floorboards. Each board runs the length of a room, and they're nailed down side by side to create the surface you walk on.
In older houses, floorboards sometimes become loose or develop gaps between them, and you might hear them squeak when someone walks over them. Mystery stories often feature loose floorboards as hiding places: a character might pry one up to stash a secret letter or treasure underneath. In The Lion, the Witch and the Wardrobe, Lucy feels the floorboards under her feet as she steps into the spare room where she discovers the wardrobe.
The term can also refer to the floor of a car, the flat surface where passengers rest their feet. When someone says to “put the pedal to the floor” or “floor it,” they mean to press the gas pedal all the way down to the floorboard to make the car go as fast as possible (safely and legally, of course).