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What’s the Plural of Diagnosis?

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A diagnosis is the “recognition of a disease from its symptoms” or the “discovery or identification of the cause of an illness or a problem”. Doctors and other professionals reach a diagnosis by observing the signs and symptoms of a disease, condition, or injury.

What is the plural of “diagnosis”?

👍🏼Usage Note

The doctor provided a detailed diagnosis after the examination. (Using the correct singular form)
Comparing several diagnoses helps determine the best treatment. (Using the correct plural form)
The medical team reviewed the different possible diagnosis. (Using the singular form when the plural “diagnoses” is required after “different possible”)
Her first diagnoses was incorrect. (Using the plural form when the singular “diagnosis” is required with the singular verb “was”)

Following Greek pluralization rules, the plural of diagnosis is diagnoses:

  • Diagnosis (pronounced dye-ahg-no-sis) is singular,
  • Diagnoses (pronounced dye-ahg-no-seaz) is plural.

As a noun, diagnosis is irregular (it doesn’t add “es”, but modifies its singular suffix by swapping the “-i” with “-e” to switch to plural).

Sentence examples
singular They are waiting for the doctor’s diagnosis.
plural They are using new methods of giving diagnoses.

English Greek nouns

Diagnoses works different. The -es suffix is not simply added or glued to the tail end of the word; rather, the -es replaces the suffix of its singular noun form, and so effectively changes the spelling and pronunciation of the entire word from singular to plural.

singular plural
crisis crises
diagnosis diagnoses
oasis oases
synopsis synopses
thesis theses
Greek nouns in English

Diagnosis is not the only Greek word in Modern English: crisis, analysis, oasis, synthesis, thesis, and nemesis all follow the same pluralization pattern.

Pro tip! An easy way to recall the plural/singular forms of nouns like crisis, diagnosis, analysis, oasis, and so on, is by remembering their Greek roots, and that Greek nouns swap to –es as a plural.

Greek makes up roughly 5% of the English language. Most English words come from the Germanic languages (Dutch, German, Old Norse, Old Frisian, and others). Still, other vocabulary is inherited from various countries and languages, and may likewise use irregular singular/plural forms.

Examples of “diagnosis” in sentences

Petitt learned of the diagnosis in the mail that Christmas Eve.

Dominic Gates, Anchorage Daily News, 27 Oct. 2022

Only 35 percent of individuals with private insurance get treatment within a year of diagnosis.

—Sandhya Raman Cq-roll Call (tns), al, 19 Oct. 2022

Confirmation of the diagnosis now takes just six hours.

—Aporva Mandavilli, BostonGlobe.com, 6 Oct. 2022

The emotional stress of a cancer diagnosis is huge, her husband expressed.

Rae Johnson, The Courier-Journal, 31 Aug. 2022

After the procedure, Breuning received a diagnosis: lung cancer.

—André-naquian Wheeler, Vogue, 24 Oct. 2022

💡Study Tip

The plural of “diagnosis,” associate it with other words ending in “-sis” that change to “-ses” for the plural, like “analysis” becomes “analyses.”.

Examples of “diagnoses” in sentences

Initially, Alzheimer’s diagnoses were only given through brain autopsies after patients died.

From the large number of facts obtained, a list of possible diagnoses can be determined, which are referred to as the differential diagnosis.

Hippocrates was known to make diagnoses by tasting his patients’ urine and smelling their sweat.

Sub-types of diagnoses include: clinical diagnosis, laboratory diagnosis, and radiology diagnosis.

Greenstick fractures are common radiological diagnoses.

Diagnosis synonyms

  • decision
  • conclusion
  • judgment
  • resolution
  • determination
  • verdict
  • finding
  • opinion
  • result

Learn about other nouns!

Worksheet

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Frequently Asked Questions

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Sources

  1. ‍ Greek percentage in English Wikipedia: medical diagnosis Diagnosis, Oxford Learner’s Dictionary, accessed on October 11, 2023. Harper, Douglas. “Etymology of diagnosis.” Online Etymology Dictionary, https://www.etymonline.com/word/diagnosis. Accessed 11 October 2023.

Grammar Expert. "Whats The Plural Of Diagnosis." GrammarFlex, Jun 1, 2025, https://www.grammarflex.com/whats-the-plural-of-diagnosis/.

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