יהוה or “YHWH” was the way the name of God was spelled in Hebrew, which apparently is hard to pronounce without vowels. The language at the time did not have written vowels, so no one knew exactly how to pronounce the name.
According to Wikipedia :
The name ceased to be pronounced in Second Temple Judaism, by the 3rd century BCE. Rabbinical Judaism teaches that the name is forbidden to be uttered except by the Kohen Gadol (High Priest) in the inner sanctum (Kodesh ha-Kadoshim, or Holy of Holies) of the Temple on Yom Kippur. Throughout the service, the High Priest pronounced the name YHWH (or Yehowah) "just as it is written" in each blessing he made.
Around the first century A.D it became normal for Jews to avoid any attempt to pronounce the name to avoid breaking the second commandment by misusing the name of God. For this reason they’d replace the name with “Adonai” whenever they encountered it while reading out. Adonai is another Hebrew word that is rendered “Lord” or “My Lord”
After the development of written vowels in Hebrew, around the 6th/7th Century Jews began to place the vowel points for “Adonai” over the consonants for “Yahweh” to remind the reader to say “Adonai” whenever he saw “Yahweh.”
Around the 13th Century the word “Jehovah” surfaced when Christian scholars took the consonants of “Yahweh” and pronounced it with the vowels of “Adonai”. This gave the sound “Yahowah” which, when latinized spelled “Jehovah”. The first recorded spelling was made by Raymundus Martini a Spanish Dominican monk in 1270.
Remember to share. God bless !