ENGLISH
REFERENCE

serum

n.
US //ˈsɪɹəm// UK //sˈɛɹəm// serum
  1. 1 skincare product (n.)
    B1 Intermediate

    a liquid skin product that has a high concentration of active ingredients to help with specific problems like dryness or aging.

    a concentrated skincare formulation designed to deliver specific active ingredients deep into the skin.

    Example

    She applies a vitamin C serum every morning before using her moisturiser.

    Example

    Dermatologists often recommend a hyaluronic acid serum for patients with persistent skin dehydration due to its high water-retention properties.
  2. 2 blood component (n.)
    C1 Advanced Technical Medicine

    the clear, watery part of blood that remains after it has clotted.

    the clear yellowish fluid that remains from blood plasma after the fibrinogen has been removed during clotting.

    Example

    The lab technician separated the serum from the rest of the blood sample.

    Example

    The patient's serum was tested for specific antibodies to determine if they had developed immunity to the virus.
  3. 3 medical treatment (n.)
    C1 Advanced Technical Medicine

    a liquid taken from the blood of an immune animal or person, used to treat or prevent a disease.

    an antiserum containing antibodies used to provide passive immunity against a specific pathogen or toxin.

    Example

    Doctors administered an anti-venom serum immediately after the snake bite.

    Example

    Before the advent of modern antibiotics, researchers relied heavily on horse-derived serum to treat life-threatening bacterial infections like diphtheria.
    • antiserum
    • antitoxin
Origin

From Latin serum (“whey”). Cognates include French sérum, Spanish suero, Italian siere, siero, Portuguese soro. Doublet of suero.

Etymology adapted from Wiktionary, available under CC BY-SA 4.0.

Last updated June 20, 2026