Hindustani, also known as Hindi-Urdu, like all Indo-Aryan languages, has a core base of Sanskrit-derived vocabulary, which it gained through Prakrit. As such the standardized registers of the Hindustani language (Hindi-Urdu) share a common vocabulary, especially on the colloquial level. However, in formal speech, Hindi tends to draw on Sanskrit, while Urdu turns to Persian and sometimes Arabic. This difference lies in the history of Hindustani, in which the lingua franca started to gain more Persian words in urban areas (such as Delhi, Lucknow and Hyderabad), under the Delhi Sultanate; this dialect came to be termed Urdu.