To niggle is to create small but persistent annoyance or discomfort, or to find unimportant faults. It conjugates to niggled, niggles, and niggling. A person can be a niggler. Its adjective form is niggling.
As a noun, a niggle, is a tiny complaint or wince of pain, or something similarly small. It is primarily used in this form outside the United States.
Side note: Another word that shares the same root is niggardly, meaning stingy. But since it sounds so similar to the racial slur, it has slowly become obsolete.
Examples
The difference in pricing for, say, female deodorant compared with the male equivalent has always niggled me, and now French feminists are petitioning supermarkets and businesses over their unfair pricing of everything from pens (who remembers the wonderful “Bic for her” that was pink and specially designed for pathetic, floppy lady-hands?) to backpacks and razors. [Huffington Post]
Whelan was asked to prove her fitness after pulling out of the 100m final at the national championships three weeks ago with a knee niggle. [Irish Independent]
For our tastes, it looks as though the house has been slightly over-renovated, but that’s a minor niggle. [Curbed]
So what are the niggling issues? [Herald Scotland]
Or choose a caviar facial or a thermal salt exfoliation; if you are fortunate, your therapist will be the delightful Arya from Bali and she will knead away all those niggling aches and knots. [Australian]
Defeat to the Panthers will bring down the curtain on an eventful career at Belmore that’s earned him the tag of niggler extraordinaire. [Sydney Morning Herald]