serum

/ˈsɪəɹəm/

//ˈsɪəɹəm// noun

By · According to Wiktionary data (CC BY-SA) ·

"serum" is a 5-letter English headword indexed on PlainSpell.

The verdict

“serum” is a moderately-common English word, ranked #10,609 in English word frequency and used as a noun.

#10,609
frequency rank, English
5
letters
7
tracked misspellings
20
confusable pairs

According to Wiktionary data (CC BY-SA, analyzed May 6, 2026) - Ellipsis of blood serum.

Visual similarity to commonly confused words

How many letter changes separate each confused pair (Levenshtein distance, normalized).

serum vs sum
60% similar
serum vs slum
60% similar
serum vs serve
60% similar

Source: PlainSpell confusable corpus (Wiktionary, CC BY-SA).

Key facts for serum
PropertyValue
Headwordserum
LanguageEnglish
Part of speechNoun
IPA/ˈsɪəɹəm/
Letters5
Frequency rank#10,609
Misspellings tracked7
Confusable pairs20
SourceWiktionary (kaikki.org)

Where “serum” sits in English frequency

Every-word frequency runs from the handful of words we use constantly (left) to the long tail used once in a blue moon (right). serum lands here:

#1#100#1K#10K#100K
← used constantlyrarely used →

Scale is logarithmic (each tick is 10× rarer). Source: FrequencyWords open word-frequency list.

Spelling & Dictionary Insight

The English entry for serum is 5 letters long, classified as a noun, and transcribed in the International Phonetic Alphabet as /ˈsɪəɹəm/. Corpus data places it at rank #10,609 in overall English word frequency, marking it as uncommon enough that many writers pause before typing it. Wiktionary records 5 distinct senses for this headword, so context determines which meaning a reader should apply.

Our generated misspelling index lists 7 likely wrong-spelling variants for serum, with forms such as "esrum", "sermu", and "serrum". Each of these forms differs from the correct spelling by one small edit: a doubled letter, a dropped silent letter, or a substituted vowel. It also participates in 20 confusable-pair relationships, "sum", "slum", "serve", and more, since the words sound or look close enough that writers reach for the wrong one mid-sentence.

Etymologically, the entry records: From Latin serum (“whey”). Cognates include French sérum, Spanish suero, Italian siere, siero, Portuguese soro. Doublet of suero. The correct English form is serum, spelled S-E-R-U-M.

Definition

  1. 1
    Ellipsis of blood serum.
  2. 2
    Blood serum used as a blood product, in the practice of medicine: blood serum from the tissues of immunized animals (human or nonhuman), containing antibodies and used to transfer immunity to another individual (human or nonhuman).
  3. 3
    A watery liquid from animal tissue, especially one that moistens the surface of serous membranes or that is exuded by such membranes when they become inflamed, such as in edema or a blister.
  4. 4
    The watery portion of certain other animal fluids, such as milk; whey.
  5. 5
    A skincare product of varying consistencies with a high concentration of one or more active ingredients, for a targeted purpose, such as preventing acne, repairing sun damage, or moisturizing.

Etymology

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

This word in other languages

suero(Español)sérum(Français)Serum(Deutsch)sérum(Português)

Common misspellings

Also misspelled as: esrum,sermu,serrum,serumm,seurm,sreum,sserum

Misspelling Pattern Breakdown

How far each generated variant is from the correct spelling of serum - expressed in single-character edits (insert, delete, or swap one letter). Bigger bars stand out at a glance; a one-edit slip is the hardest to catch.

esrum2sermu2serrum1serumm1seurm2sreum2sserum1
Edit distance from "serum"

Definitions, pronunciation, and etymology for this entry are drawn from Wiktionary via the kaikki.org structured extract (CC BY-SA); frequency ordering uses the FrequencyWords open word-frequency list (2018 English corpus, MIT). See the methodology for how each field is sourced and updated.

Frequently Asked Questions

How do you spell "serum"?
"serum" is spelled S-E-R-U-M. The IPA pronunciation is /ˈsɪəɹəm/.
What does "serum" mean?
As a noun, "serum" means: Ellipsis of blood serum.
What words are commonly confused with "serum"?
"serum" is commonly confused with "sum", "slum", "serve". These words look or sound similar but have different meanings. PlainSpell provides detailed comparisons for each pair.
How do you pronounce "serum"?
The IPA (International Phonetic Alphabet) transcription for "serum" is /ˈsɪəɹəm/. Click the speaker icon on the pronunciation badge above to hear it spoken aloud where audio is available.
What is the origin of the word "serum"?
From Latin serum (“whey”). Cognates include French sérum, Spanish suero, Italian siere, siero, Portuguese soro. Doublet of suero. See the full etymology section above for more details.
Is PlainSpell free to use?
Yes, PlainSpell is a completely free word reference. You can look up definitions, pronunciations, confusable pairs, homophones, and spelling corrections across 5 languages without any sign-up or subscription.

Using “serum”

The practical upshot for anyone who landed here from a spell-check.

  • The one correct English spelling is S-E-R-U-M - every other letter order is a misspelling in standard orthography.
  • Say it as /ˈsɪəɹəm/ (IPA); tap the speaker on the pronunciation badge to hear it where audio exists.
  • Don't mix it up with “sum” - see the side-by-side comparison. serum vs sum
  • Browse more English words and confusable pairs in the same reference. English words
Data Source

Wiktionary (via kaikki.org), licensed under CC BY-SA & GFDL. Word ordering uses an open word-frequency list; misspelling variants are generated by edit-distance from the correct headword.

Source: Wiktionary (via kaikki.org) Structured Wiktionary extract

Source: FrequencyWords open word-frequency list FrequencyWords open word-frequency list