Definition of "parenthesis"

parenthesis

/pəˈɹɛnθəsɪs/

noun
countable and uncountable, plural parentheses
1. A clause, phrase or word which is inserted (usually for explanation or amplification) into a passage which is already grammatically complete, and usually marked off with brackets, commas or dashes.
2. Either of a pair of brackets, especially round brackets, ( and ) (used to enclose parenthetical material in a text).
  Quotations
  There be five manner of points and divisions most used among cunning men; the which if they be well used, make the sentence very light and easy to be understood, both to the reader and hearer: and they be these, virgil,—come,—parenthesis,—plain point,—interrogative […] it is a slender stroke leaning forward, betokening a little short rest, without any perfectness yet of sentence.
  1824, John Johnson, Typographia, Or the Printer's Instructor, London: Longman, Hurst, Rees, Orme, Brown and Green
  Whoever introduced the several points, it seems that a full-point, a point called come, answering to our colon-point, a point called virgil answering to our comma-point, the parenthesis-points and interrogative-point, were used at the close of the fourteenth, or beginning of the fifteenth century.
  1842, F. Francillon, An Essay on Punctuation‎, page 9
  [T]he present research also made an effort to approach a greater accuracy in presenting the original sources of borrowed words. This was achieved by presenting etymons from Hindustani in the Devanagari script followed by a transliteration in the Roman alphabet in parentheses.
  2018, James Lambert, “Anglo-Indian slang in dictionaries on historical principles”, in World Englishes, volume 37, page 255
3. (rhetoric) A digression; the use of such digressions.
  Quotations
  Mr. Trevanion was one of those talkers, who are too much engrossed with their own subject matter to have much attention to bestow elsewhere; with them silence is attention. Ethel's wandering eye, and lip, tremulous with its effort to speak, would never have attracted his notice. To his utter astonishment, she interrupted a parenthesis, as brilliant as the rocket which it depicted, by saying,—"Mr. Trevanion, I do not know what you will think of my boldness, but I must speak to you."
  1837, L[etitia] E[lizabeth] L[andon], chapter XV, in Ethel Churchill: Or, The Two Brides. […], volume II, London: Henry Colburn, […], page 113
  Ryan Bingham (George Clooney): I thought I was a part of your life. Alex Goran (Vera Farmiga): I thought we signed up for the same thing […] I thought our relationship was perfectly clear. You are an escape. You're a break from our normal lives. You're a parenthesis. Ryan Bingham (George Clooney): I'm a parenthesis?
  2009, Up in the Air
4. (mathematics, logic) Such brackets as used to clarify expressions by grouping those terms affected by a common operator, or to enclose the components of a vector or the elements of a matrix.