I pulled this excerpt off of a site...however I've found other sites that have basically said the same information, that the word Jehovah is a combination of YHWH and adonay which is a hebrew worf for lord...they would take the a-o-a from adonay and mix it with YHWH creating YaHoWaH.
Early in their relationship, Moses asked God to reveal His name. God readily complied with Moses' request by giving Him not one but TWO names of God...
Name #1 - The first name that God told Moses about was Hayah . Hayah is a Hebrew word meaning I AM. Part One of this analysis discusses Hayah .
Name #2 - The second name that God told Moses about was YHWH. YHWH is a Hebrew word for which we have only the four consonants. We do NOT have the vowels. Ergo, we aren't quite sure what YHWH means, or how to pronounce it. Part Two of this analysis discusses YHWH.
Moreover God said to Moses, "Thus you shall say to the children of Israel: 'The LORD (YHWH ) God of your fathers, the God of Abraham, the God of Isaac, and the God of Jacob, has sent me to you. This is My name forever , and this is My memorial to all generations.'" Ex 3.15
The Usage of Jehovah Came From Catholicism
By combining the vowel signs of 'Adho . nay and 'Elo . him' with the four consonants of the Tetragrammaton the pronunciations Y e ho . wah' and Y e howih' were formed. The first of these provided the basis for the Latinized form "Jehova(h)." The first recorded use of this form dates from the thirteenth century C.E. Raymundus Martini, a Spanish monk of the Dominican Order, used it in his book Pugeo Fidei of the year 1270. Hebrew scholars generally favor "Yahweh" as the most likely pronunciation.(6) Aid to Bible Understanding, Watchtower Bible And Tract Society, 1971, pp. 884, 885.Please note: Hebrew scholars generally favor "Yahweh" as the most likely pronunciation.
Bruce Metzger, who criticizes the KJV's misusage of Jehovah, gives additional information:
The form "Jehovah" is of late medieval origin; it is a combination of the consonants of the Divine Name and the vowels attached to it by the Masoretes but belonging to an entirely different word .... (1) The word "Jehovah" does not accurately represent any form of the Name ever used in Hebrew. (2) The use of any proper name for the one and only God, as though there were other gods from whom the true God had to be distinguished, began to be discontinued in Judaism before the Christian era and is inappropriate for the universal faith of the Christian Church.
I know it's a little choppy, but some food for thought.