This little word stretches from stupidity to wisdom, from religion to science, and from dark deeds to light.
Let's start with the stupidity, as that's easiest to spot. In Britain a nit is someone who's done something a bit stupid. It's short for nitwit.
Sadly, the word is quite rarely used nowadays. People now are much more likely to be numpties than nitwits.
As for the wisdom, well, the Egyptian godess Nit was rather wonderful. She was goddess of all sorts of things - war and hunting and weaving, as well as wisdom. She was so wise she was even roped in to try to sort out the other Egyptian gods' disputes, which wasn't easy with that lot. In her spare time she was often to be seen either nursing a baby crocodile (er...and she was supposed to be wise???) or else wearing one of her spare heads, which came in the shape of a lion's head, a cow's, or a snake's.
Nit is the one on the right.
Nits are the eggs of lice, as well, though in Britain, Australia and New Zealand the term nits usually includes the lice themselves, particularly if they're headlice.
A nit is also a unit of luminance equal to one candela per square metre. Or it can be a unit of information equal to 1.44 bits.
In Australia nit is keeping watch, especially during a criminal activity.
Lastly, there are quite a few schools, especially in India, called the National Institute of Technology. It may be true that their acronym, NIT, means stupid, but hey, I think that's just nit-picking.
Spot the frippet: nit. The word meaning louse comes from the Old High German hniz; the unit of luminance comes from the Latin nitor, which means brightness; the unit of information comes from N(aperian Dig)it; and the Ozzie on watch comes from nix, which is from the German nichts, which means nothing.