Core (noun)

1. The central or innermost part of something, often of a round shape.
2. The most important or essential part of something.
3. The central part of a fruit around which the seed is located.
4. The central or innermost layer of the Earth, consisting of solid iron and nickel.
5. A removable central cylindrical part of a computer's microprocessor, containing the most advanced components.

Origin:

The word "core" comes from the latin word "cor", meaning "heart". the term was first used in the 14th century to describe the central or innermost part of something.

Examples:

1. An apple's core contains the seeds.
2. The core of the problem is the lack of communication.
3. The Earth's core is over 5000°C.
4. The computer's core was updated to improve performance.
5. She cut the core out of the pineapple to prepare it for juicing.