parenthesis - n.
(pl. parentheses)
1 a a word, clause, or sentence inserted as an explanation or afterthought into a passage which is grammatically complete without it, and usu. marked off by brackets or dashes or commas. b (in pl.) a pair of round brackets () used for this.
2 an interlude or interval.

in parenthesis as a parenthesis or afterthought. [LL f. Gk parenthesis f. parentithemi put in beside]