pron.
 nothing.
exclam.
  - expressing denial or refusal.
 - Brit. dated used as a warning that a person in authority is approaching. 
[perh. from the obs. phr. keep nix ‘to watch, guard’.]
 
v.
 chiefly N. Amer. put an end to; cancel:
 he nixed the deal.
 
  Etymology
  C18: from Ger., colloq. var. of nichts ‘nothing’.