Using the word "Khuda" for Allah Rab-ul-Izzat
The word "Khuda" is a word of the Persian language, which to some extent is a translation of Wajib-ul-Wujood (the Necessarily Existent). Its use for Allah Rab-ul-Izzat has been ongoing from the elders of the Ummah, therefore its use for Allah Ta'ala is permissible. However, since this word is neither a substitute for "Allah" (Ism-e-Zat) nor equal to it, using His Personal Name "Allah" for the pure essence of Allah is the best. (Aham Masail/Vol:5/Pg:54)