To mark or indicate as a flat note in music; to flatten a note.
From 'bemol' (the musical term) as a verb, following the pattern of musicological terminology where nouns can become verbs (e.g., 'to flat', 'to sharp').
In medieval music notation, musicians needed verbs for adjusting pitches—'bemole' was their technical term, and it shows how specific professions create their own linguistic worlds that the general public never uses.
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