What's meant by "nominative" in grammar?

Menna Basha
"Nominative" generally refers to the case of the grammatical subject in most languages, often--but not necessarily--pertaining to the agent or "doer" of the action of the main verb. In some languages, the nominative case has specific inflection, as in Latin "amicus videt amicum" '(the) friend sees (a) friend' where the nominative ending "-us" marks the first instance of the noun "amic-" as the grammatical subject of the sentence whose verb is "videt" 'sees', in contrast to the accusative case ending "-um" which marks the second occurrence as the direct object of the verb. (And because languages like Latin rely so heavily on inflection to mark sentence roles, word order is much freer, i.e., one could also convey the same meaning '(the) friend sees (a) friend' by various permutations of "amicus videt amicum," e.g. "amicus amicum videt," "amicum amicus videt" and "videt amicum amicus.")
In other languages, however, like English, the nominative case/role is not specifically marked but is more a functional designation. Thus in "The friend sees his friend," both the instances of "friend," i.e., as the heads of the noun phrases "the friend" and "his friend," respectively, are identical morphologically and it is only the word order that tells us that the first "friend" is the subject or is used in the (really nonexistent) "nominative case" and the second, which comes after the transitive main verb, is in the accusative or "objective" case. (One exception to the general principle that English has no case inflection is with personal pronouns. Take for example "He sees him" where "He," as the grammatical subject, obligatorily shows "nominative" case, whereas "him," as the direct object, is in the objective/accusative case, which in fact consists here of the use of a morphologically distinct or "suppletive" form; compare also the nominative/objective pairs "I"/"me," "she"/"her," "we"/"us" and "they"/"them," which also evince suppletion, i.e., one can hardly make the argument that there is a distinct "accusative" inflection in English.)
Finally, it should be noted that the so-called "nominative" case may be used for other sentence elements besides the grammatical subject. With linking verbs, for example, the element coming after the verb is usually described as the subject complement in that it is normally co-referential with the subject, e.g., "I am his friend" where "his friend," unlike in the example in the previous paragraph, is here said to be in the "predicative nominative." This analysis had led many authorities to insist that in a sentence like "It is me," the objective "me" is "incorrectly" used and should be replaced by the nominative "I," but this contradicts centuries of actual English usage.