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What’s the Plural of Diagnosis?

Diagnosis plural is diagnoses. Singular is diagnosis.

What’s the plural of “diagnosis”?

A diagnosis is the “discovering or identifying the cause of an illness or a problem”:

  • Diagnosis (pronounced dye-ag-no-sis) is singular;

  • Diagnoses (pronounced dye-ag-no-seaz) is the only plural form of diagnosis.

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

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

English Greek nouns

Here’s the thing: diagnosis as a plural does in fact end in –es, i.e., diagnoses. Why is diagnoses still seen as irregular when it conforms to the norm and uses -es as a plural noun? See from the nouns above that each one adds an -s or -es to go from singular to plural.

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.

Greek nouns in English

Diagnosis is not the only Greek word that endures in Modern English: crisis, analysis, oasis, synthesis, thesis and nemesis, (there are more), all follow that same conversion of -is as a singular to –es plural. A pro tip: recognizing the pattern these words follow (crises, diagnoses, analyses, syntheses and oases) is the most effective way to learn and remember their proper singular and plural forms!

As it happens, Greek takes up roughly 5% of the English language. Most English words come from the Germanic languages, (Dutch, German; Old Norse; Old Frisian, and others), but many others are brought down from various countries and languages, and continue to stand the test of time.

Examples of “diagnosis” (singular) 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,, 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

Examples of “diagnoses” (plural) 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

Read about other plural nouns


  1. Greek percentage in English
  2. Wikipedia: medical diagnosis
  3. Diagnosis, Oxford Learner’s Dictionary, accessed on Oct 11, 2023.
  4. Harper, Douglas. “Etymology of diagnosis.” Online Etymology Dictionary, Accessed 11 October, 2023.

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