Animal

noun

1. In scientific usage, a multicellular organism that is usually mobile, whose cells are not encased in a rigid cell wall (distinguishing it from plants and fungi) and which derives energy solely from the consumption of other organisms (distinguishing it from plants).

   "A cat is an animal, not a plant. Humans are also animals, under the scientific definition, as we are not plants."

2. In non-scientific usage, any member of the kingdom Animalia other than a human.
3. In non-scientific usage, any land-living vertebrate (i.e. not fishes, insects, etc.).
4. A person who behaves wildly; a bestial, brutal, brutish, cruel, or inhuman person.

   "My students are animals."

5. A person of a particular type.

   "He's a political animal."