According to the Oxford English Dictionary, the correct plural is
"viruses". Tom Christiansen of Perl.com presents the OED's
abbreviated entry for the word:
" Etymology: a. L. virus slimy liquid, poison, offensive odour or
taste. Hence also Fr., Sp., Pg. virus.
1 Venom, such as is emitted by a poisonous animal. Also fig.
2 Path. a A morbid principle or poisonous substance produced in the
body as the result of some disease, esp. one capable of being
introduced into other persons or animals by inoculations or otherwise
and of developing the same disease in them. Now superseded by the next
b Pl. viruses. An infectious organism that is usu. submicroscopic, can
multiply only inside certain living host cells (in many cases causing
disease) and is now understood to be a non-cellular structure lacking
any intrinsic metabolism and usually comprising a DNA or RNA core
inside a protein coat (see also quot. 1977). [ Formerly referred to as
filterable viruses, their first distinguishing characteristic being
the ability to pass through filters that retained bacteria.] "
What's the Plural of `Virus'?
In the "Classical Inflections" portion of his paper, he explains in
detail the classical linguistic reasons for this. (Due to copyright
restrictions, I cannot reproduce his entire treatise here.}
He goes on to say:
"Virus is not attested in the plural in Latin, and is of a rare form
(2nd declension neuter in -us) that makes it debatable what the Latin
plural would have been; the only plural in English is viruses.
Omnibus and rebus were not nominative nouns in Latin. Ignoramus was
not a noun in Latin."
What's the Plural of `Virus'?
Jonathan de Boyne Pollard explains:
"The convention for forming the plural of Latin words in English is to
use the Latin plural form, or, if Latin does not actually have a
plural form for the word, to form the plural in the normal manner used
for other English words.
So, for example:
* The plural of basis is bases. basis is a third declension
noun with the nominative singular ending in -is. The nominative plural
of such nouns ends in -es.
* The plural of ignoramus is ignoramuses. ignoramus is not a
singular word in Latin. It isn't even a noun. It is a verb, and
already in the plural. (It means "we do not know". This is the first
person plural.) So one forms its English plural by appending -es.
virus is a second declension noun ending in -us. (It can be translated
to "slime", "poison", "venom", or "stench".)
However, it is one of the few such nouns that has no plural in Latin.
It occurs only in the singular. So, just as with ignoramus, one forms
its English plural by appending -es."
The plural of virus is viruses.
Dictionary.com rather dryly concurs:
"Q. What is the plural of virus?
It is not viri, or (which is worse) virii. True, the word comes
directly from Latin, but not all Latin words ending in -us have -i as
their plural. Besides, viri is the Latin word for 'men' (plural of
vir, man, the root the English virile). There is in fact no written
attestation of a Latin plural of virus."
What is the plural of virus?
Perhaps of interest: In one discussion (which I am prohibited from
linking to here because the URL is obscene), people who refer to
viruses as "viri" or "virii" were rather derisively referred to as
"idiot script kiddies". Ouch.
I hope this helps!
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