Nott was a longtime Death Eater (HBP20) who stunned by Hermione early on during the Battle of the Department of Mysteries (OP35). He was then injured by the falling shelves of prophecies, as Lucius Malfoy demanded the other Death Eaters leave him to continue the battle. Since Nott did not reappear in Voldemort’s ranks after that battle, the injury was either serious enough to put him out of commission, or Nott was disenchanted by the Death Eaters’ abandonment and left the fighting to the other, younger, Death Eaters.
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.
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).