The quality or state of being beguiling; the characteristic charm or appeal that beguiles.
From 'beguiling' (present participle of 'beguile') + '-ness' (suffix creating abstract nouns meaning 'the quality of'). The '-ness' suffix is one of English's oldest noun-makers, used since Anglo-Saxon times.
Words ending in '-ness' are how English speakers nominalize almost anything—'beautiful' becomes 'beauty' (from French) or 'beautifulness' (from English), and we have both words, which is why English is delightfully redundant.
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