Nit/nɪt/ Definition 1 of 4Pro Tip 1/2Insect Life Stage Think of 'nit' as a developmental stage, like a caterpillar before it becomes a butterfly. I used a special shampoo to remove all the nits. Pro Tip 2/2Singular and Plural 'Nit' remains the same whether you're talking about one or many, like 'sheep' or 'fish'. My vet found a nit on my dog's fur.