If we put you inside a box and told you to think of a name for a cat, could we tell what the name was by looking at the cat? No, we'd have to open up the box and look at (or listen to ) you. Ditto for any similar game, like creating slang, interchanging meanings, creating private spellings, doing math and then giving names to important theorems, etc.

This only works for (at least partly-) intentional definition though - if your definition of red is to point at a stop sign, then a fire truck, then a tomato, and then to point at grass and say "not this," then we can't figure out your meaning for red just by looking at what's inside the box. First we have to get the definition from you, and then we have to go look at stop signs and fire trucks.

So depending on how you want to cash out "meaning," it can be in your mind, or in your mind+context. But it's not just in the outside world, because there's no way an alien knows what to call a capybara just from examining one.