the.com/nit

means A tiny, often trivial flaw or detail — or the louse egg it's literally named for, the thing people pick at when they 'nitpick.'

from From Old English 'hnitu,' meaning louse egg, with ancient roots stretching back through Germanic languages to a very old Indo-European word for the same small nuisance. The literal insect-egg sense is old and unglamorous; the figurative 'nitpicking' — fussing over tiny, picky details — grew naturally from the image of someone painstakingly combing through hair for something barely visible.