Nominative

The nominative case is a grammatical case for a noun, which generally marks the subject of a verb, as opposed to its object or other verb arguments.

In Latin this is the noun itself without inflexion, in that form as you know it: Tullius, Livia, Cicero, forum, lex, consul are in singular nominatve.

Nominative in plural

The plural of Latin nouns is, however, more difficult. Here are the basic and very general rules for making a plural nominative:

• If a word ends in "-us", then the plural nominative ends in "-i". Tribunus becomes tribuni.
• If a word ends in "-a", then the plural nominative ends in "-ae". Provincia becomes provinciae.
• If a word ends in "-o", then the plural nominative ends in "-ones". Legio becomes legiones.
• Many other words change their ending to "-es", whose rules are more difficult and are not detailed here. Here are some just for example:

consul in plural nominative becomes consules,

lex in plural nominative is leges,

mos is mores,

virtus is virtutes,

homo is homines.

• Some common nouns ending in "-us" change to long "-ús" in plural nominative , for example:

magistratus in plural nominative is magistratús,

exercitus in plural nominative is exercitús and so on.

• Nouns of the neutral gender which often end in "-um" have a plural nominative ending in "-a". So forum becomes fora. Examples with other endings:

ius in plural nominative becomes iura,

caput becomes capita.

Usage in practice

Not only Nova Roman citizens but every educated people use sometimes Latin plurals in the English language, so it is very important to learn some plural forms. You can start it by studying the article about addressing magistrates.