Pronunciation note: The i is pronounced with a long e sound. The o is a short o sound. The e is silent. The level of pretentious French accent used to pronounce it is up to you. SEE-SOHN.
Spelling note: There is no c in sissone. It has nothing to do with scissors. The skill should actually be spelled sissonne with two n’s as it is named after the Count of Sissonne, a region in France. For whatever reason, when the element came from ballet into gymnastics, it lost an n. So, if you choose to spell it with two n’s, that is also acceptable and probably more correct, but no one in gymnastics does it.
The difference between the sissone and the split jump comes in both the angle of the split (in a sissone, the 180-degree split is supposed to be hit at a 45-degree angle and is done so exactly 0% of the time) and the landing. The sissone lands on one foot, the split jump on two.
Because of the need for simple A dance elements to fulfill the dance combination requirement and because of (from 2013-2016) the bonus achieved by connecting A dance elements out of D acrobatics, the sissone has been among the most popular dance elements on beam, though in 2017 it was left behind by the split jump when it graduated to a B rating and has been slowly falling out of favor ever since.