From Wikipedia...
The word derives from the Bengali word biletī, (older sources mention a regional Hindustani language but the use of b replacing v is found in Bengali and not Urdu) meaning "foreign",[4] which more specifically came to mean "European", and "British; English" during the time of the British Raj.[5] The Bengali word is a loan of Indian Persian vilāyatī from vilāyat meaning "Iran" and later "Europe" or "Britain",[6] ultimately from Arabic wilāyah ولاية "state, province".