nominative case

showing the subject of a verb (Grammar)

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. (Basically, it is a noun that is doing something, usually joined (such as in Latin) with the accusative case.)
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Noun
1. the category of nouns serving as the grammatical subject of a verb
(synonym) nominative, subject case
(hypernym) case, grammatical case