Sleetier is an adjective used to describe an increased level of sleet or the formation of a sleet-like substance. Some synonyms for sleetier include slushier, icier, more frozen, more icy, and more packed. These terms can be used interchangeably to describe weather conditions where the precipitation is a mixture of rain and snow, or during cold conditions where water droplets freeze upon contact with the ground, creating a thin layer of ice. All of these words are perfect when describing winter weather that is dangerous and slippery, so it's important to be careful when traveling on roads and sidewalks during these conditions.