[NR4U] "Not right for you"

[NS] "Nice shot"; used sincerely in competitive and cooperative online games […]

[NSFW] "Not safe for work"; indicates that one should avoid using […]

[NT] "No text"; used on Internet forums or Usenet to indicate […]

[nth] See: [TO THE NTH DEGREE].

[NTH] "Not totally here"

[nuisance] See: [PUBLIC NUISANCE].

[nuke] {v.} To fix any meal in a microwave oven. * […]

[nuke a tater] {v. phr.} 1. To bake a potato in […]

[null and void] {adj.} Not worth anything; no longer valid. * […]