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.
Spelling note: There is no c in sissone. It has nothing to do with scissors.
The difference between the sissone and the split jump comes in both the angle of the split (the 180 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 remains among the most popular dance elements on beam.