The majority of voters this past week were correct in saying that snirt is a noun. Snirt is found in the Midwest at the end of winter. It is the combination of snow and dirt found on the side of roads and in parking lots. The word (snirt) itself, which is a combination of the words snow and dirt, is what is considered a portmanteau word. Portmanteau words are those that are formed by combining the sounds and meanings of two different words. They are considered a linguistic blend.
The reason this type of linguistic blend is called a portmanteau word comes from the meaning of the word portmanteau. A portmanteau is a type of bag or suitcase used in Europe that carries mixed items. Thus a portmanteau word carries a mix of words.
Slithy (lithe and slimy) and mimsy (flimsy and miserable) are some well known portmanteau words created by Lewis Carroll that appear in "Through the Looking Glass."