Ambiguous Words

English has words where the "correct" plural depends on context, dialect, or domain. Plurality picks one default for each, but the right answer for your application may differ. This guide documents known ambiguities and shows how to override them with Plurality.Custom.

penny / pence

penny has two valid plurals with different meanings:

• pennies — individual coins ("I found three pennies on the ground")
• pence — monetary amount ("That costs fifty pence")

Plurality defaults to pennies via suffix rules.

# Override for British monetary usage
defmodule MyApp.Inflection do
  use Plurality.Custom,
    irregulars: [{"penny", "pence"}]
end

staff

staff is treated as uncountable (collective noun: "the staff are..."), which is the standard British English usage. If you need the countable sense (multiple groups of employees, or walking staffs):

defmodule MyApp.Inflection do
  use Plurality.Custom,
    irregulars: [{"staff", "staffs"}]
end

opera / opus

opera is its own word (the musical art form), not just the plural of opus. Plurality treats opera as a standalone base form. If your domain treats it as the plural of opus:

defmodule MyApp.Inflection do
  use Plurality.Custom,
    irregulars: [{"opus", "opera"}]
end

trachea

Plurality defaults to the modern English plural tracheas. The classical Latin form tracheae is used in medical contexts but is too niche for the built-in default:

defmodule MyApp.Inflection do
  use Plurality.Custom,
    irregulars: [{"trachea", "tracheae"}]
end

kibbutz / kibbutzim

The Hebrew plural kibbutzim is standard in discussions of Israeli settlements, but Plurality defaults to the anglicized form kibbutzes:

defmodule MyApp.Inflection do
  use Plurality.Custom,
    irregulars: [{"kibbutz", "kibbutzim"}]
end

Acronyms (API, CPU, URL)

Plurality.pluralize("API") returns "APIS" because the engine applies ALL CAPS style preservation. There is no reliable way to distinguish acronyms from regular words in ALL CAPS without a dictionary lookup, and any heuristic would break normal ALL CAPS behavior (LEAF -> LEAVES, BOX -> BOXES).

Override specific acronyms as needed:

defmodule MyApp.Inflection do
  use Plurality.Custom,
    irregulars: [
      {"api", "apis"},
      {"cpu", "cpus"},
      {"url", "urls"},
      {"sdk", "sdks"}
    ]
end

axe / axis

Both axe and axis pluralize to axes. Plurality treats axis as the canonical singular because it is more common in technical and business English. This means singularize("axes") returns "axis", making the axe -> axes -> axis path lossy.

If your domain works with axes (the tools):

defmodule MyApp.Inflection do
  use Plurality.Custom,
    irregulars: [{"axe", "axes"}]
end

Rare compound nouns

Common head-noun compounds like mother-in-law, attorney general, and court-martial are handled in the built-in irregulars. Rarer ones are an endless list — override as needed:

defmodule MyApp.Inflection do
  use Plurality.Custom,
    irregulars: [
      {"lady-in-waiting", "ladies-in-waiting"},
      {"commander-in-chief", "commanders-in-chief"},
      {"man-of-war", "men-of-war"}
    ]
end

Applying overrides

Call the custom module from code that needs the domain-specific behavior:

MyApp.Inflection.pluralize("cowfish")  #=> "cowfish"
MyApp.Inflection.pluralize("formula")  #=> "formulae"

See the Customization guide for full details.