From WordNet (r) 3.0 (2006) [wn]:
zodiac
n 1: a belt-shaped region in the heavens on either side to the
ecliptic; divided into 12 constellations or signs for
astrological purposes
2: (astrology) a circular diagram representing the 12 zodiacal
constellations and showing their signs
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Zodiac \Zo"di*ac\, n. [F. zodiaque (cf. It. zodiaco), fr. L.
zodiacus, Gr. ? (sc. ?), fr. ?, dim. of zw^,on an animal,
akin to ? living, ? to live.]
[1913 Webster]
1. (Astron.)
(a) An imaginary belt in the heavens, 16[deg] or 18[deg]
broad, in the middle of which is the ecliptic, or
sun's path. It comprises the twelve constellations,
which one constituted, and from which were named, the
twelve signs of the zodiac.
(b) A figure representing the signs, symbols, and
constellations of the zodiac.
[1913 Webster]
2. A girdle; a belt. [Poetic & R.]
[1913 Webster]
By his side,
As in a glistering zodiac, hung the sword. --Milton.
[1913 Webster]