What is the word that is replaced with a noun or a pronoun?

Answer 1

All nouns can be replaced by pronouns. If you mean what do you call a noun that is replaced by a pronoun, the answer is antecedent.

Answer 2

The noun for which a pronoun is substituted is called the pronoun antecedent.

The noun for which the pronoun is substituted is called its antecedent (preceding, prior) because the noun is mentioned either earlier in the sentence or in a preceding sentence.

Personal pronouns like he she me we are used instead of somebody's name.

e.g. I like Jon, he is very interesting.

(the pronoun he substitutes for the proper noun Jon).

Personal pronouns can also be substituted for noun phrases.

e.g. My sister and I went to the beach. We both got sunburned.

(the pronoun we substitutes for the noun phrase my sister and I)

Answer 3

A noun (or noun phrase) or a pronoun replaces a noun.

Examples:

Martha, my neighbor, gave me the flowers. (the noun 'neighbor' replaces the noun 'Martha' as an appositive)

Martha has a garden. She gave me the flowers. (the pronoun 'she' replaces the noun 'Martha' as the subject of the second sentence)