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3.17 Plural forms of nouns

Note the following singular and plural forms:

  • addendum
    • addenda
  • alumna
    • alumnae
  • alumnus
    • alumni
  • analysis
    • analyses
  • antenna
    • antennae (feelers) or antennas (aerials)
  • appendix
    • appendixes (or appendices)
  • bacterium
    • bacteria
  • basis
    • bases
  • bureau
    • bureaus
  • bus
    • buses
  • census
    • censuses
  • crisis
    • crises
  • criterion
    • criteria
  • ellipsis
    • ellipses
  • erratum
    • errata
  • focus
    • focuses (not focusses, which is the preferred verb form)
  • formula
    • formulas (or formulae)
  • gas
    • gases (not gasses, which is the verb form)
  • hypothesis
    • hypotheses
  • index
    • indexes (of a book) or indices (in mathematics, statistics)
  • matrix
    • matrices
  • medium
    • (medium or media) (check dictionary for plural form to use in a given context)
  • memorandum
    • memorandums (or memoranda)
  • nucleus
    • nuclei
  • parenthesis
    • parentheses
  • phenomenon
    • phenomena
  • plateau
    • plateaus
  • surplus
    • surpluses
  • symposium
    • symposiums (or symposia)

Many other English words form their plurals irregularly, including some of those ending in y, o, f and fe.