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.

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