Brief summary of the meaning, origin and etymology of the word "Jehovah":
This pronounceable form of YHWH was introduced in 1520 by Galatinus but immediately strongly contested. Because the Hebrew script only has consonants, the vowels had to be inserted when the text was read out loud. When the language ceased to be used, the Masoretes devised an ingenious vowel-notation system to preserve the pronunciation. However, the name YHWH was deemed so holy that it shouldn't be pronounced. Instead, the reader would say (adonai), meaning My Lord, from the untranslated root ('adon 27b).
Hence the Masoretes superimposed the vowel-notation of [adonai] on to [YHWH] and the word Jehovah was born.
(http://www.abarim-publications.com/Meaning/Jehovah.html)
An even briefer summary: The word "Jehovah" is an amalgamation of the Tetragrammaton (consonants) and "Adonai" (vowels), making a BRAND NEW WORD.