Is "moister" a word?

Earlier today, a colleague asked if "moister" is a word. I was suffering from Monday-morning brain at the time, so turned to my trusty online Oxford dictionary, where I was pleasantly surprised to find this gem of an example sentence:

"The artist would have given him a moistly sensuous mouth, but this man's modest lip is all but covered by a warm brown beard, carefully clipped and combed."

It certainly made me chuckle. Beard anyone?