Wizards, Witches and Beings: N
Nearly Headless Nick 
Gryffindor House ghost. The nickname of the ghost of Sir Nicholas de Mimsy Porpington, a wizard who died in a botched execution on October 31, 1492. (More...)
Nettles, Madam Z.
Madam Z. Nettles of Topsham, along with D.J. Prod, was apparently a happy customer of Argus Filch's Kwikspell course. Before Kwikspell, she "had no memory for incantations and my potions were a family joke!" (CS8)
Nigellus, Phineas (SEE Black, Phineas Nigellus)
Nott (wizard) 
A longtime Death Eater (HBP20) stunned by Hermione early on during the Battle of the Department of Mysteries (OP35). His son is Theodore Nott, a Slytherin in Harry’s year (JKR).
The word "not" has an obvious negative connotation, which is fitting for a Death Eater. See entry below for more possibilities.
Nott,
Theodore 
(b. circa 1980)
Slytherin, 1991 - 1998 (PS7, OP26)
Son of the Death Eater Nott, Theodore
is described as "weedy-looking"
(OP26) and “a clever loner who does not feel the need to join gangs, including Malfoy’s.” He can see thestrals (
JKR).
Nott's name could have many different meanings: nothing (as
in 'naught'), and binding (as in 'knot'). In Norse myth, Nott is the "personification
of night, and the daughter of Narvi. Nott's chariot is pulled by the
horse Hrimfaxi ('frost-maned') which covers the earth with dew early
in the morning."
(EM).
Nutcombe,
Honoria 
(1665 - 1743)
Founded the Society for the Reformation of Hags (fw47).
Honoria was Wizard of the Month on Rowling's website for August, 2004 (JKR).
