Select the word which means the same as the group of words given.
Unit of weight for precious stones

The correct answer is Carat.

Let us break down the meanings of the given options to understand why "Carat" is the correct choice:

1. Carat: A unit of weight used for measuring precious stones and pearls (equivalent to 200 milligrams). It is also used to express the purity of gold (though spelled "karat" in some regions).
2. Pure: Not mixed or adulterated with any other substance or material; clean and free from contamination.
3. Accurate: Correct in all details; exact.
4. Reliable: Consistently good in quality or performance; able to be trusted.

Therefore, the word that means the same as the group of words "Unit of weight for precious stones" is Carat.