Serum

How to spell serum

5 letters · 2 syllables

How to pronounce serum

Say the part in capitals loudest.

What does serum mean?

1. nounThe clear, pale yellow fluid that separates from blood when it clots, or a medical preparation derived from it.
2. nounA concentrated liquid skincare product applied to the face before moisturiser.

Serum in a sentence

• The laboratory spun the sample to separate the serum from the red cells.

• She patted a vitamin C serum onto her cheeks each morning.

• Doctors administered an antivenom serum after the snake bite.

• The new hydrating serum promised to reduce fine lines.

Where does serum come from?

Language of origin: Latin

This word was taken directly from the Latin serum, which literally meant 'whey', the thin watery liquid that separates from milk when it curdles. Roman writers used it more broadly for any thin, watery bodily fluid, and that sense is what English borrowed in the late seventeenth century when physicians needed a name for the pale liquid that remains after blood has clotted. From that medical anchor the meaning widened: a 'serum' came to mean a fluid used to immunise or treat, such as antivenom or a vaccine preparation, and more recently a concentrated liquid skincare product. The spelling stayed close to the Latin original, with a single 'r' and the final '-um' typical of borrowed Latin neuter nouns. Because the second syllable is an unstressed schwa, writers sometimes hesitate over the vowel, but the steady Latin form is a reliable guide.

How the word is built

• serum (from Latin serum: whey, the watery part of a fluid); an unanalysable root borrowed whole