NBs

'NBs'

[niobium.n.01] as in: a soft grey ductile metallic element used in alloys; occurs in niobite; formerly called columbium

'NBs'

[nota_bene.n.01] as in: a Latin phrase (or its abbreviation) used to indicate that special attention should be paid to something

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Examples:
the margins of his book were generously supplied with pencilled NBs