In the Oxford Dictionary of English, Third Edition, 2010, both print as well as online editions (https://en.oxforddictionaries.com/definition/assamese have given the definition of the word 'Assamese' as --

noun: 1A native or inhabitant of Assam.

2 mass noun: The Indic language which is the official language of Assam, related to Bengali and spoken by around 23 million people, roughly half in Assam and half in Bangladesh.

This is grossly untrue, as Assamese as a language is not related to Bengali, although both have similar scripts. Further, Assamese is spoken by people of Assam and never by the people of Bangladesh. Therefore, the dictionary version that 23 million people, roughly half in Assam and half in Bangladesh, speak Assamese is a gross and unpardonable mistake on the part of the editors of the most trusted dictionary in the world. We would like to request the Oxford authorities to undertake research on the issue, find the facts and actual figures, and rectify the mistake immediately.