1. To take food into the mouth, to chew it, and then to swallow it: Marcus and Margaret are striving to maintain good health by being careful to eat healthy foods and not eat too much.

Another word that means to eat is "to consume food".

When William's little girl wanted more dessert, he told her that she had eaten enough.

2. To gnaw or to or to devour: While the Oliver family was on vacation, termites had eaten some of their wooden furniture.
3. To destroy by corroding or wearing away: Jim was told that the acid he was using to clean the rust spots on his car eats metal; so, he should be careful that he doesn't use too much of it or spill any of it on other parts of the surface of his vehicle.
4. Etymology: from Indo-European ed-, "eat" which produced the basic word for "eat" in many European languages.

From Greek edein and Latin edere, "to eat".