The property of being capable of being read, legibility.(noun)
The property of being easy or engaging to read.(noun)
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Use "readableness" in a sentence
"But the reviewer is not asked to state whether he finds Mr. Hocking readable so much as to state the kind of readableness at which Mr. Hocking aims and the measure of his success in achieving it."
"It does not add to a writer's readableness if readers are pulled up now and again to wonder -- Why this distortion?"
"These little sketches have been written to supply what seemed to the author a real need, -- a volume which should give clearly, compactly, and with a fair degree of readableness, the stories connected with the surviving old houses of New England."