Nabi means Prophet without or without a significant Book, Hazrat means Moth Mr. or Mrs.
While Rasool means a Prophet with a Significant Book.

hazrat is an Arabic word actually. Urdu is a combination of many languages like hindi ,farsi,arabic,turkish ,english and many more languages .Hazrat has been taken from arabic and now it is also an urdu word. As Arabs inwaded Iran , persian was very much affected by arabic and hazrat is also used in farsi(persian now).
Hazrat in Arabic means Mr./Mrs.which is used for an honourable person.