1. To become covered in or coated with ice. If the temperature drops any more, the steps will definitely ice up overnight.
2. To cause something to become covered in or coated with ice. In this usage, a noun or pronoun can be used between "ice" and "up." The frigid temperature iced the steps up overnight.
ice something up
to cause something to become icy. I hope the cold doesn't ice the roads up.The wind and rain iced up the roads.
ice up
to become icy. Are the roads icing up?
ice up
v.
1. To become covered with ice: The road has iced up, so be careful.
2. To cause something to become covered with ice: The storm has iced up the bridges. The cold weather iced the pond up, so we decided to go skating.