What type of noun is the word "wet" when it is used as a noun?
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Not common as a noun, I think-- but I suppose it would be an uncountable concrete noun of quality:
The wet entered into my bones and I contracted arthritis.
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Additionally, here's a handy guide to noncount nouns:
http://www2.gsu.edu/~wwwesl/egw/noun...nt.htm#Liquids