Serum (noun)

1. A clear, yellowish fluid that separates from blood when it clots.
2. A liquid containing proteins that is extracted from blood or blood plasma and used in various medical treatments.
3. A liquid containing a concentrated form of a beneficial substance, especially a nutrient or a medication, that is applied to the skin or taken orally.

Origin:

Serum is derived from the latin word "sērum" meaning whey or fluid.

Examples:

1. The doctor ordered a serum test to check for infection.
2. The serum is used to help the patient's immune system fight the disease.
3. The serum contains antioxidants that will nourish the skin.
4. The serum was injected into the patient's bloodstream.
5. The serum is a concentrated form of vitamin C.