Custodial, in family law, is about who has custody of someone, especially a child — who the child lives with, who makes the big decisions. The custodial parent is the one the child lives with; the other parent is non-custodial. Courts talk about custodial rights. The same idea of holding a person appears in criminal law: a custodial sentence means you go to prison, not just pay a fine. Though actually there is a further, different job use that trips people up: custodial staff are the people who clean and look after a building. That one is about caretaking, not about children or court. The child-and-court sense is the centre of this word as learners meet it; the prison sense sits next to it; the cleaning sense is the odd one out.