-um in Latin
Latin nouns ending in -um regularly formed their plurals in -a. These include such words as curriculum, which gives the plural curricula. A datum is a singular item of data. 'Datum' is a word rarely used in English - though data are essential for academic writing! (The word 'datum' is rather like 'a singular statistic'.) In mapmaking and related subjects, it means 'a base line'.
A particular ending which can be found in academic English is -anda. sometimes -enda. This is (these are) plural forms: in the singular the '-a' ending is replaced by '-um'. The '-nd-' element of these words indicates '[something] which ought to be [done]'. So '-nda' indicates 'the things which ought to be done'. See for example addenda, corrigenda and agenda. If you only have one of the item in question, the words should be addendum, corrigendum and agendum.