This Internet Slang page is designed to explain what the meaning of NIT is. The slang word / acronym / abbreviation NIT means . Internet Slang. A list of. Define nit. nit synonyms, nit pronunciation, nit translation, English dictionary definition of nit. abbr. National Invitational Tournament n. The egg of certain parasitic. Define nit: the egg of a louse or other parasitic insect also: the insect itself when young.