The nominative case (abbreviated NOM) is one of the grammatical cases of a noun or other part of speech, which generally marks the subject of a verb or the predicate noun or predicate adjective, as opposed to its object or other verb arguments. Generally, the noun "that is doing something" is in the nominative, and the nominative is the dictionary form of the noun.
Nominative comes from Latin cāsus nominātīvus "case for naming", which was translated from Ancient Greek ὀνομαστικὴ πτῶσις, onomastikḗ ptôsis "inflection for naming", from onomázō "call by name", from ónoma "name". Dionysius Thrax in his Art of Grammar refers to it as orthḗ or eutheîa "straight", in contrast to the oblique or "bent" cases.
Linguistic characteristics 
The reference form (more technically, the least marked) of certain parts of speech is normally in the nominative case, but this is often not a complete specification of the reference form, as it may also be necessary to specify the number and gender. Thus the reference or least marked form of an adjective might be the nominative masculine singular. The parts of speech which are often declined and therefore may have a nominative case are nouns, adjectives, pronouns and less frequently numerals and participles. The nominative case often indicates the subject of a verb but sometimes does not indicate any particular relationship with other parts of a sentence. In some languages the nominative case is unmarked, it may be said to be marked by a zero morpheme. Moreover, in most languages with a nominative case, the nominative form is the lemma; that is, it is the reference form used to cite a word, to list it as a dictionary entry, etc.
Nominative cases are found in Slovak, Ukrainian, Hungarian, Lithuanian, Georgian, German, Latin, Greek, Icelandic, Old English, Old French, Polish, Czech, Romanian, Russian, and Pashto, among other languages. English still retains some nominative pronouns, which are contrasted with the accusative (comparable to the oblique or disjunctive in some other languages): I (accusative, me), we (accusative, us), he (accusative, him), she (accusative, her), they (accusative, them) and who (accusative, whom). A usage that is archaic in most, but not all, current English dialects is the singular second-person pronoun thou (accusative thee). A special case is the word you: Originally, ye was its nominative form and you the accusative, but over time you has come to be used for the nominative as well.
In active–stative languages there is a case sometimes called nominative which is the most marked case and is used for the subject of a transitive verb or a voluntary subject of an intransitive verb but not for an involuntary subject of an intransitive verb; since such languages are a relatively new field of study, there is no standard name for this case.
Subjective case 
Some writers on English grammar employ the term subjective case instead of nominative to draw attention to the differences between the "standard" generic nominative and the way it is used in English.
Generally, when the term subjective case is used, the term objective is used for the oblique case, which covers the roles of accusative, dative, and objects of a preposition. The genitive case is then usually called the possessive form and often is not considered as a noun case per se; English is then said to have two cases, the subjective and the objective. This view is an oversimplification, but it is didactically useful.
The nominative case marks the subject of a verb. When the verb is active, the nominative is the person or thing doing the action (agent); when the verb is passive, the nominative is the person or thing receiving the action.
- The boy saw her.
- She was seen.
Predicate noun or adjective 
The nominative also marks things equal to the subject (that is, a predicate noun or adjective).
- Socrates was a wise man.
- Socrates was wise.
- nominativus. Charlton T. Lewis and Charles Short. A Latin Dictionary on Perseus Project.
- ὀνομαστικός. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at Perseus Project
- Dionysius Thrax. τέχνη γραμματική (Art of Grammar), section ιβ´ (10b): περὶ ὀνόματος (On the noun). Bibliotheca Augustana.
- German nominative case A lesson covering the nominative case in the German language
- The Nominative Case - Russian Grammar A lesson covering the nominative case in the Russian language