nit [nit] the egg of a louse. nit (nit), 1. The ovum or hatched egg of a body, head, or crab louse; the egg is attached to human hair or clothing by a layer of chitin. 2. A unit of luminance; a luminous intensity of 1 candela per square meter of orthogonally projected surface. [A.S. knitu] nit (nit) the egg of a louse. nit (nĭt) n. The egg of certain …