in French, singular 'un adieu', plural 'les adieux'
The foreign plural form of symposium is symposia, while the English plural form is symposiums.
Forum---Plural Form Forums,Foreign Plural Form Forumina
the word emphasis is already singular because when in foreign plural it is emphases
The plural of syllabus is syllabi.
Genii. However, it is often confused with the being that came out of Aladdin's lamp so people often say 'geniuses' to avoid confusion! This is according to my grandad, who is a genius!
The foreign plural form of symposium is symposia, while the English plural form is symposiums.
In English, "adieu" does not have a commonly used plural form, as it is borrowed from French and typically used as a singular farewell. However, if one were to refer to multiple farewells, one might informally say "aduies" or simply use "goodbyes" instead. Ultimately, the context in which "adieu" is used often dictates whether a plural form is necessary.
The plural form of addendum is addenda
Forum---Plural Form Forums,Foreign Plural Form Forumina
The plural form of apparatus is apparatuses. It has no foreign plural.
data IS the plural form of datum.
The singular form is bacterium; the plural form is bacteria.
the word emphasis is already singular because when in foreign plural it is emphases
The plural of syllabus is syllabi.
There are several possible plural forms of the English word cherub, which is a word of Hebrew origin. The one I think you are referring to is cherubim, which is derived directly from the Hebrew plural. Cherubs and cherubims also occur in English.
Ova is the plural form. The singular form is ovum.
There are several plural forms of the word octopus: Octopuses is the most often used form cited in references in the US, but other forms are accepted such as octopi and octopodes.