nit [OE] A nit is the tiny egg of a human head louse, and was in use for something small or insignificant by Shakespeare’s day. However, nitwit is not recorded until the 1910s and nit-picking or pedantic fault-finding did not come into the language until the 1950s. The idea here is of painstakingly searching through someone’s hair for nits. In Australia children shout ‘nit!’ to warn their friends when a teacher is approaching. The person who is keeping watch is said to keep nit. Nit is this context is probably an alteration of nix [L18th], which comes from German nichts, ‘not’.