Think about all of the cultural training that goes behind a word.
When we use a word like fish, it now contains, for most speakers, all of the knowledge gained by biology, and thus no longer contains whales as it used to.
So the knowledge and perception of a culture is imbued in a name when it is taught to a person. Words are never learned absent from context, usually in multiple contexts, and often with some sort of education involved.
“This is a mushroom. It’s a fungus. Funguses look like plants but they’re more closely related to animals. They’re different because of the tough material they’re made out of and they’re colonial organisms.”
That’s not what someone living non-modernly in a jungle would pass onto a child when explaining the name ‘mushroom’, but it is a part of our enculturation in modern societies. (Not that the former couldn’t read about it on Wikipedia with their Google Blimp connected iPad. The future is now.)
So we don’t all learn the exact same thing with a word, and we can’t come up with a perfect, exculsivizing description of a word, but the definitions we learn overlap enough for understanding and to facilitate easy learning of facts or meanings we haven’t learned before. It is having this functional basis in common that allows us to communicate imprecisely, while at the same time highly functionally.
Every content word has a conversation behind it. A story. Cultural information that was exchanged to pass on that word.
The causal chain of a word is mimetic, steeped in knowledge of the world, which is used to create the conception of the word. As knowledge changes, the definitions of the “same” word change.