Staircase
A staircase is an indoor hill with corners, and always has one more step than you think in the dark.
Empty glass
An empty glass is a full glass of nothing, and optimists and pessimists have argued about it for 3,000 years.
Chair
A chair is furniture for sitting on, unless it is in a bedroom, where it is furniture for clothes to sit on.
Door
A door is a wall that can be opened, and is labelled ‘push’ on the side you will try to pull.