점점 and 서서히 both stand for 'gradually'. However, they are not a synonym. 점점: 점(漸)+점(漸). 漸 = progress toward a certain direction little by little 서서히: 서(徐)+서(徐)+-히(adverbial suffix). 徐 = (go) slowly Therefore, 점점 more focuses on 'little', while 서서히 on 'slow'. When things progress little by little, then they will do so slowly. That's why the two words can be used interchangeably, but the nuance is ..