The mathematical concept and number representing the absence of quantity....
The branch of biology that studies the animal kingdom....
A school of Mahayana Buddhism emphasizing meditation and direct experience over theoretical study....
A type of rigid airship named after German Count von Zeppelin, popular in the early 20th century....
A landlocked country in southern Africa known for Victoria Falls and ancient ruins....
The king of the Olympian gods in ancient Greek religion and mythology....
A chemical element essential for human health, used in alloys and as a dietary supplement....
Any disease or infection naturally transmissible from vertebrate animals to humans....
A mosquito-borne virus causing mild illness in adults but serious birth defects in pregnant women....
A postal code system used by the United States Postal Service....