Simple definitions in dictionaries — an example

In a good English dictionary, the definitions are simple, but still useful. Look at the difference between a complicated definition and a simple explanation of the word ear:

ear = the organ of hearing and equilibrium in vertebrates, in mammals consisting of an external ear (...), a middle ear (...), and a liquid-filled inner ear, with sensory nerve endings for hearing and balance. —Random House Webster’s Electronic Dictionary

Everybody knows what ears are. Why is this definition so complicated? It could look like this:

Your ears are the two parts of your body, one on each side of your head, with which you hear sounds. —Collins COBUILD English Dictionary

This definition uses simpler words than the first one. It doesn’t use difficult, scientific words like equilibrium and vertebrates. This definition is a real English sentence — it sounds like a friend who is explaining a word to you. It is very easy to understand.