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.
Reference:: Sikh Philosophy Network http://www.sikhphilosophy.net/discourses-in-english/8304-ek-omkar.htmlReference:: Sikh Philosophy Network http://www.sikhphilosophy.net/showthread.php?t=8304
Guru ji saya Oankaar brahma utpat...so lets take Guru Ji's WORD for the cprrect pronounciation of EK Oankaar
Jarnail singh gyani