The quality or state of being comprehensible; the characteristic of being able to be understood.
From comprehensible plus the abstract noun suffix -ness. While grammatically valid, 'comprehensibility' is the more standard modern form.
Comprehensibleness is beautifully awkward—it's the kind of word that shows how English could theoretically add -ness to almost anything, creating long Latinate stacks that eventually get replaced by simpler forms!
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