"The American Heritage Dictionary says mazel tov comes from Mishnaic Hebrew and ultimately from Akkadian, one of the earliest written languages: manzaltu, mazzaztum meant ‘position of a star’, from izuzzu ‘to stand’. The related words Mazzaroth and mazalot have to do with astronomical constellations or the zodiac in Kabbalistic astrology."

(Source: stancarey.wordpress.com)