Please note: Latin Declension Rules
The Nominative Case (cāsus nōminātīvus) is the subject case. There is nothing very tricky about it. When you look up a noun (in Latin 'noun' is nōmen which is traditionally defined as a part of speech that names persons, places or things) in a Latin-English dictionary, the first form you see is the Nominative Singular. The same is true of pronouns, which stand in place of nouns and adjectives (modifiers of nouns and pronouns), both of which are also subject to declension.
In English, some words are only used in the plural, but these are few and far between. The same is true in Latin.
For the vast majority of Latin nouns, the form you see in the dictionary is the Nominative Singular, followed by an ending for the genitive, and the gender of the noun. (Note: What you see following the initial word is slightly different for adjectives and pronouns.)
Nominative Singular Example: Puella
(1) Dictionary form: Puella, -ae, f. - girl
That shows you the nominative singular for the Latin for girl is "puella". As in English, "puella" can be used for the subject of a sentence.
(2) Example: The girl is good - Puella bona est.
Nominative Plural and Paradigms
As is true for the other cases, the Nominative Case can be used in both the singular and the plural. For puella, that plural is puellae. Traditionally, paradigms put the Nominative Case at the top. In most paradigms, the singulars are in the left column and the plurals in the right, so the Nominative Plural is the top right Latin word.
Nominative Case Abbreviation
Nominative is usually abbreviated Nom.. Since there is no other case beginning with an "n", it can be abbreviated N.
Note: Neuter is also abbreviated "n", but neuter is not a case, so there is no reason to be confused.
Nominative Forms of Adjectives
Just as the dictionary form of the noun is the Nominative Singular, so it is also for the adjectival form. Usually the adjectives have a Nominative Singular masculine followed by either feminine and then neuter, or just neuter in words where the masculine is also the feminine form.
Compare:This adjective dictionary-style entry shows that the masculine singular of the Nominative Case is bonus. The feminine singular of the Nominative Case is bona as was shown in the example about the girl (puella bona est.) An example of a third declension adjective showing the masculine/feminine form and the neuter is:
(3) Noun: puella, -ae 'girl'
(4) Adjective: bonus, -a, um 'good'
(5) Finalis, -e - final
Nominative With To Be Verbs
Had I selected the sentence "The girl is a pirate," both the words for girl and pirate would be nouns in the Nominative Singular. That sentence would be "puella pirata est." Pirate is a predicate nominative. The actual sentence was "puella bona est" where both the noun for girl, puella, and the adjective for good, bona, were in the Nominative Singular. "Good" is a predicate adjective.