A (23) | B (24) | C (45) | D (19) | E (25) | F (18) | G (15) | H (14) | I (14) | J (2) | K (3) | L (9) | M (15) | N (11) | O (10) | P (34) | Q (3) | R (22) | S (30) | T (14) | U (3) | V (9) | W (7) | Z (2)
Old World

Animals from Asia and Africa. For example, Old World monkeys are those native to Asia or Africa.

Olfactory

The sense of smell.

Omnivore

An animal that eats all kinds of foods, both plants and animals.

Opposable thumb/toe

The first digit can be moved so that it can touch each of the other digits. It is used to grasp items.

Organic

Something that is raised or grown without synthetic fertilizers, pesticides, or drugs.

Organism

Anything that is alive.

Ornamental plumage

On a bird, colorful feathers that do not blend into the surrounding environment as camouflage. These colors are often used to attract a mate.

Ossicones

Hair-covered horns found on the heads of giraffes. Ossicones are made of bone and are part of the skull.

Oviparous

Producing eggs that develop and hatch outside the body.

Ovoviviparous

Producing young from eggs that hatch inside the body. Some snakes, such as the common boa, give birth this way.