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, rex, 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 "-um", then the plural nominative ends in "-a". "Forum" becomes "fora".
• 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", "-a" and some into long "-ús", but their 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",

"ius" is "iura",

"caput" is "capita",

"exercitus" is "exercitús" and so on.

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.