key, n. /kiː/ 1. A small device for opening what has not yet been closed. 2. The interval between the last person's life in a house and the first person's life in the same house. 3. (music) The tonal centre around which all domestic noise resolves: drill-whine in F, carpet adhesive peeling in B♭, a toddler's footfall establishing the tonic. 4. A unit of weight equal to one adult's inability to hold all the days inside one day. 5. (archaic) The tooth-shaped prayer you carry in your pocket when you are building something that does not exist yet from something that no longer does. 6. The only object that means both "here" and "gone."