/peuh ren"theuh sis/ , n. , pl. parentheses /-seez'/ .
1. either or both of a pair of signs ( ) used in writing to mark off an interjected explanatory or qualifying remark, to indicate separate groupings of symbols in mathematics and symbolic logic, etc.
2. Usually, parentheses . the material contained within these marks.
3. Gram. a qualifying, explanatory, or appositive word, phrase, clause, or sentence that interrupts a syntactic construction without otherwise affecting it, having often a characteristic intonation and indicated in writing by commas, parentheses, or dashes, as in William Smith - you must know him - is coming tonight.
4. an interval.
[ 1560-70; parénthesis a putting in beside. See PAR-, EN- 2 , THESIS ]