What is the meaning of niggling?

verb

• Worry unnecessarily or excessively.
  • usage: "don't fuss too much over the grandchildren-they are quite big now"
  • synonyms: fuss, niggle, fret
• Argue over petty things.
  • usage: "Let's not quibble over pennies"
  • synonyms: quibble, niggle, pettifog, bicker, squabble, brabble

adjective

• Informal) small and of little importance. (
  • usage: "a fiddling sum of money"; "a footling gesture"; "our worries are lilliputian compared with those of countries that are at war"; "a little (or small) matter"; "a dispute over niggling details"; "limited to petty enterprises"; "piffling efforts"; "giving a police officer a free meal may be against the law, but it seems to be a picayune infraction"
  • synonyms: fiddling, footling, lilliputian, little, piddling, piffling, petty, picayune, trivial