What is the meaning of Niet?

Alternative spelling of nyet.

not, no, don't: used to express negation.

staple (wire fastener)

inflection of nieten:

  1. first/second/third-person singular present indicative
  2. imperative

first/second/third-person singular present indicative

imperative

not

nothing

third-person singular present indicative of nīedan

night

Source: wiktionary.org