Transliterated Hebrew word: from ancient commentary on Job 38:32, which has מזרות mazarot. But 2 Kings 23:5 (corresponding to IV Kingdoms 23.5 LXX) has מזלות mazalot, which is the more common form; and the Septuagint has μαζουρώθ in both places. Mazarot may be a very unusual variant for mazalot, which means the 12 constellations. Notice the Vulgate to 2 Kings 23:5, which explicitly says the 12 constellations. (note from Raphael Finkel).
Extensive notes on this word are available at web site 1. On the zodiac, see Suda zeta 123, epsilon 2824, kappa 2654; on the dog star, see sigma 285.