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Latin plurals

Plurals of Latin words used in English are formed according to the rules either of the source language (apex/apices, stratum/strata) or of the borrowing language (gymnasium/gymnasiums, arena/arenas). In some cases more than one form is in use, sometimes with a usage distinction (appendix/appendices/appendixes, formula/formulae/formulas) and sometimes with no clear distinction (cactus/cacti/cactuses). Words ending in -is usually follow the original Latin form (basis/bases, crisis/crises) for reasons of euphony, and the same rule operates in other cases (nucleus/nuclei). A more alien form is the plural -mata of words ending in -ma in the singular (lemma/lemmata, stigma/stigmata). There are occasional surprises; for example we might expect the plural of crux to be (Latin) cruces but it is in fact more often (English) cruxes. There is a trap for the unwary with Latinate nouns ending in -us which cannot form plurals in -i for formal grammatical reasons: hiatus (a fourth-declension noun in Latin with a plural hiatus), ignoramus (a first-person plural verb in Latin, not a noun), octopus (a Romanized form of a Greek word octopous), vademecum (cum being a preposition meaning ‘with’). The table below shows the types of plural that the more commonly used Latin words have in English; when there is more than one both are shown:

singular form

latin-type plural

english plural

addendum

addenda

alga

algae

apex

apices

apexes

appendix

appendices

appendixes

aquarium

aquaria

aquariums

arena

arenas

automaton

automata

automatons

basis

bases

cactus

cacti

cactuses

codex

codices

compendium

compendia

compendiums

corrigendum

corrigenda

crematorium

crematoria

crematoriums

crisis

crises

crux

cruces

cruxes

desideratum

desiderata

encomium

encomia

encomiums

focus

foci

focuses

formula

formulae

formulas

genus

genera

gymnasium

gymnasia

gymnasiums

helix

helices

helixes

index

indices

indexes

lemma

lemmata

lemmas

matrix

matrices

matrixes

maximum

maxima

maximums

memorandum

memoranda

memorandums

miasma

miasmata

minimum

minima

minimums

momentum

momenta

momentums

moratorium

moratoriums

nucleus

nuclei

oasis

oases

radix

radices

referendum

referenda

referendums

stigma

stigmata

stigmas

stratum

strata

thesis

theses

vortex

vortices

vortexes

Further information will be found in the separate entries for some of these words

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