Symmetry
Symmetry was the state of being identical on both sides.
In 2151, after examining an irregular crater created by an explosive detonated on Archer's Comet, Malcolm Reed expressed his wish that it had been more symmetrical. (ENT: "Breaking the Ice")
Later that year, Doctor Phlox, while studying the results of his cosmetic surgery on Jonathan Archer, noted that Akaali Archer's anterior crests weren't quite symmetrical and was about to fix them, when Archer said it (his disguise) didn't have to be too perfect. (ENT: "Civilization")
In 2373, Odo encouraged a Changeling infant to feel the symmetry of a sphere he was teaching it to mimic. (DS9: "The Begotten")