nut

noun

A hard, dry, indehiscent, usually single-seeded fruit, having a hard and bony, or woody or leathery mesocarp; the outermost endocarp may be fibrous or slightly fleshy. Many nuts are enclosed in a cup-shaped structure, the cupule. The term nut is often loosely used of any hard fruit. For example, the walnut and coconut are in fact drupes and the Brazil nut is a seed.