1. to find fault with in a petty way; to criticize minor details
2. to cause slight but persistent annoyance or discomfort

Examples

• She niggled about every small mistake in the report.
• The teacher niggled over proper comma placement.
• A small doubt niggled at the back of his mind.
• The pain in her shoulder niggled throughout the day.
• He niggled about the color of the curtains for weeks.
• Something about his story niggled her, but she couldn’t say what.