origins
The word is of Latin origin and the plural is addenda.
Plateaus is acceptable. The word is of French origin, so the strict plural ought to be plateaux.
The plural form of the noun analysis is analyses. It is the standard plural form for a word of Greek origin ending in -is.
The plural form of the noun thesis is theses. It is the standard plural form for a word of Greek origin ending in -is.
Alumnus is singular; alumni is plural. The origin of the word alumnus is Latin and uses the Latin plural form.
ΑΙΜΟΒΟΡΟΙ / αιμοβόροι (plural, male). ΑΙΜΟΒΟΡΑ / αιμοβόρα (plural, neutral). This is the translation for the literal meaning of this word which seems to be of Greek origin (this must be the root-word).
In English, "venuses".In Latin, which is the word's language of origin, the plural is veneres.
No, the word "bureaux" is not Flemish. It is actually of French origin and is the plural form of "bureau," which means a desk or an office. In Flemish, the equivalent word would be "burelen" or "kantoren."
Animalia is the plural of the Latin word animal. It comes from anima, which originally meant "breath".
Datum is latin for "That which is a given, that which is taken for granted." Its plural is the more common "Data."
The word "bag" is from Old Norse or a similar Scandinavian origin. It was used in the early 13th century. The ending "-s" was added to make the word plural. Please see the related link below.
I believe the latin word for star is "stella". Stellae is the plural form.