abbreviation of Latin nota bene "note well," 1670s.
Entries linking to n.b.
nota bene
a Latin phrase meaning "mark well, observe particularly," 1721, from Latin nota, second person singular imperative of notare "to mark" (from nota "mark, sign, note, character, letter;" see note (n.)) + bene "well" (see bene-). Often abbreviated N.B.