Easy isn't it? everyone knows what "eat" means.
Except I'm not sure there is agreement. We probably all agree that to eat, one puts food in the mouth, masticate (chew) and swallow. But is even this true? It works for any animal with a mouth. But if we look at protozoans (unicelled organisms similar to animals, they were previously classified as animals, until 2005), they have no mouths. So when they take in food, is it incorrect to say they "eat", so are we required to say they "consume" or "injest"? There's a word, "zoophagy", which means "to eat meat". There are fungi that are zoophagous, so, by definition, those fungi "eat meat". But fungi don't have mouths implying that eating doesn't require a mouth. Then, when a fungus is zoophagous, it can only obtain food by inserting a part of itself (a hypha, a bit like a root) into the food source (an animal) and digesting it, then to absorb the resultant soup of nutrients. Therefore, zoophagy, "to eat meat", seems to require digestion to take place (one of the most common uses of the term "zoophagy" is with regard to fungi, so it seems that to eat without having a mouth is a common understanding). So, does eat' include digestion or exclude it? I've checked the Oxford Dictionaries (OED, COED) and they do not help. While they seem to define eat well, they give no information to prove their definition is valid (it excludes digestion). Certainly, OEDs would exclude digestion so that means they would require that we do not apply the term "eat" to protozoa or fungi (but scientists do).
So, this simple little question is in fact very complicated. What does "eat" mean?
Thanks if you're brave enough to have a really good stab at this. All logical answers and appropriate citations appreciatively received. Happy to be guided from philosophical perspective (logic) or from a pure linguistic perspective or both.
(PS My current opinion as a non-linguist is that, based on fungi, "to eat" must include digestion and needn't involve a mouth, mastication or swallowing. Please do not let my position bias your thoughts.)