Djlilli Answered First
An interjection has no real value in grammar, they are usually spoken, less often written. Words such as 'Oh', 'Ah', 'Hey', 'Hi', 'Hmmm', 'Eh?' are all interjections
In Grammar

Is neither a interjection?

An interjection is an exclamatory word like Hey! or Whoops! or Yipes!   'Neither' can be a conjunction, an adjective or a pronoun. See related link.

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Is an interjection an emotion?

  No, an interjection is used to express an irrepressible emotion by "interjecting" words like Hey! or Ouch! or Holy Cats! into a sentence without affecting its grammar.

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In Grammar

What is interjection noun?

  Interjection nouns are words that express strong feelings.   example: wow, Ouch, Oh

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