Much of what we're covering isn't to do with the required words not existing, but to do with the fact that they're not available to you at the time

Thing is, you can train yourself to get around that as marnameow remarks above. When a word doesn't exist at all, the problem you have is with the listener. It's not too bad if you're in the kind of 1-1 conversation where you can get continuous feedback from the person you're talking to. In other cases you end up having to substitute a sentence or even a paragraph or worse still you end up being completely misunderstood.

First example that springs to mind: no male noun corresponding to "tart". Of course in the modern world a lot of people would simply apply it to men anyway, but I wanted to pick a suitably uncontroversial one.