If someone is weak, they are not healthy or do not have good muscles, so that they cannot move quickly or carry heavy things.

If someone has an organ or sense that is weak, it is not very effective or powerful, or is likely to fail.

If you describe someone as weak, you mean that they are not very confident or determined, so that they are often frightened or worried, or easily influenced by other people.

If you describe someone's voice or smile as weak, you mean that it is not very loud or big, suggesting that the person lacks confidence, enthusiasm, or physical strength.

If an object or surface is weak, it breaks easily and cannot support a lot of weight or resist a lot of strain.

A weak physical force does not have much power or intensity.

If individuals or groups are weak, they do not have any power or influence.

A weak government or leader does not have much control, and is not prepared or able to act firmly or severely.

If you describe something such a country's currency, economy, industry, or government as weak, you mean that it is not successful, and may be likely to fail or collapse.

If something such as an argument or case is weak, it is not convincing or there is little evidence to support it.

A weak drink, chemical, or drug contains very little of a particular substance, for example because a lot of water has been added to it.

Your weak points are the qualities or talents you do not possess, or the things you are not very good at.

You can say that someone has a weak chin to indicate that their chin is not large, especially when you want to suggest that they do not have a strong character.