The word is Oankaar....because this word occurs in Gurbani...but not "omkaar" meaning there is no such word. The Hindu word is OM - not omkaar...
Guru Ji "invented" the open OORRa as KAAR...and coined the enw word oankaar and added EK befoe it.
Guru ji saya Oankaar brahma utpat...so lets take
Guru Ji's WORD for the cprrect pronounciation of EK Oankaar
Jarnail singh gyani