An adjective describing a young child who has learned to use the toilet, and so no longer needs nappies (diapers). It is almost always used with 'be' or 'get': "She's toilet-trained now," "He got toilet-trained at two." Note it describes a state the child has reached, not something happening right now — that's 'toilet-training'. The word is normal, everyday family language, not medical or rude; parents say it to each other, doctors say it to parents, and nursery teachers ask it on forms. Americans often say 'potty-trained' instead, which sounds warmer and more childlike; 'toilet-trained' is the more common British form and the more neutral one. People also use it of pets, especially cats, though 'house-trained' is more usual for dogs. Used of an adult, it becomes an insult — saying someone is 'not toilet-trained' means they behave crudely.