1. Either or both of the upright curved lines, ( ), used to mark off explanatory or qualifying remarks in writing or printing or enclose a sum, product, or other expression considered or treated as a collective entity in a mathematical operation.
2. 1. A qualifying or amplifying word, phrase, or sentence inserted within written matter in such a way as to be independent of the surrounding grammatical structure.
   2. A comment departing from the theme of discourse; a digression.
3. An interruption of continuity; an interval: "This is one of the things I wasn't prepared for-the amount of unfilled time, the long parentheses of nothing" (Margaret Atwood).

[Late Latin, insertion of a letter or syllable in a word, from Greek, from parentithenai, to insert : para-, beside; see para-¹ + en-, in + tithenai, to put.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.