Snice is a portmanteau of the words 'snow' and 'ice'. As you might suspect, it is a mixture of slushy snow and ice. As it happens, the word 'snice' is most often found in use as a technical term -- an obscure bit of jargon used by those who construct ice palaces and the like.

Most snice is artificially concocted; it is white and comparatively soft, but is wet enough to bind into sturdy ice structures given time to 'set'. It may either be used as a type of mortar between ice blocks, or be sprayed into forms which are removed once it has set - essentially, snice is ice cement. Sadly, although snice is frequently used in the Nordic nations and Canada (where ice hotels and the like are exciting tourist attractions), the recipe for construction-grade snice is not openly available on the internet.

I was not able to find a definite origin of the word, but it may have been coined by Ake Larsson, the architect of the IceHotel in Swedish Lapland.