Most nouns in English are made into plural nouns by adding an ‘s’ to the singular form. If the noun ends with an s, ch, sh, or x, an ‘es ‘ is added to make the noun plural. Plural nouns that are not made plural in this way are irregular plural nouns .
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SINGULAR PLURAL
alumnus alumni
cactus cacti
focus foci/focuses
fungus fungi/funguses
nucleus nuclei
radius radii
stimulus stimuli
SINGULAR PLURAL
axis axes
analysis analyses
basis bases
crisis crises
diagnosis diagnoses
ellipsis ellipses
hypothesis hypotheses
oasis oases
paralysis paralyses
parenthesis parentheses
synthesis syntheses
synopsis synopses
thesis theses
SINGULAR PLURAL
appendix appendices
index indeces/indexes
matrix matrices/matrixes
SINGULAR PLURAL
beau beaux
bureau bureaus/bureaux
tableau tableaux/tableaus
SINGULAR PLURAL
child children
man men
ox oxen
woman women
SINGULAR PLURAL
bacterium bacteria
corpus corpora
criterion criteria
curriculum curricula
datum data
genus genera
medium media
memorandum memoranda
phenomenon phenomena
stratum strata
SINGULAR PLURAL
deer deer
fish fish
means means
offspring offspring
series series
sheep sheep
species species
SINGULAR PLURAL
foot feet
goose geese
tooth teeth
SINGULAR PLURAL
antenna antennae/antennas
formula formulae/formulas
nebula nebulae
vertebra vertebrae
vita vitae
SINGULAR PLURAL
louse lice
mouse mice
.
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I found the list of the irregular nouns quite interesting and even referencial.Thanks for the effort.