Zealot: n.:
someone committed to the other side.

Zebra: n.:
a jackass in pinstripes which does not work in an office.

Zen: n.:
a Buddhist sect that teaches that the path to enlightenment is not to strive to find the path to enlightenment.
The Beatniks picked up on the "not to strive" part and left the rest for the Buddhists.

Zero: n.:
nought.
One reason the Government uses budget figures with all those zeros is to show you they've got you by the noughts.

Zero tolerance: motto:
total intolerance.

Ziggurat: n.:
a pyramid rendered in low-resolution graphics.

Zigzag: adj.:
showing the straightforwardness of a political compromise, or a legal decision.

Zinc: n.:
the alternative-medicine wonder drug of the '90s, having edged out selenium. In danger of being displaced by magnesium.
Since the Nixon years, the primary component of copper pennies.

Zionist: n.:
one who denies the humanity of Palestinian arabs.

Zipper: n.:
a post-Victorian mechanical contrivance that allows couples to undress more rapidly.

Zither: n.:
Hippie harp.

Zodiac: n.:

1. the mandala of astrology.
   
2. a brand of hotrod rubber rafts.

Zombie: n.:
a mixed drink that creates replicas of its namesake. The next morning, you feel a lot as though you had died on a Caribbean island.

Zoo: n.:

1. a place where people go to show off to a captive audience of animals.
   
2. a municipal replica of the halls of Congress.

Zwieback: n.:
dry milktoast.

Zygote: n.:
chicken to the gamete's egg.