parenthesis - definition and synonyms

noun [countable] 

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  1. 1
    a word, phrase, or sentence that is not directly related to what you are saying or writing but is added to give more information
  2. 2
    [usually plural] one of the two symbols ( and ), used in writing for separating a word, phrase, or number from the rest of a sentence
    in parentheses:

    The studentsnationalities are shown in parentheses.