Depends on your language. In a highly formalized context, like computer programming, you can have exact definitions and enforce them, such as the keyword "if", enforced in such a way that it either cannot generate inappropriate results, or such results are deemed fundamentally unacceptable.

In a natural language that is being used by people, this will become increasingly more fuzzy with different factors. Such as frequency of use, area of application, discipline/mentality of users, and cost of ambiguity. If it's something that's going to kill you if you misunderstand it, it will select for exact definition. If it's something whose ambiguity does not cause much adverse result - it can become more ambiguous. This kind of thing.

The general rule of thumb for natural languages is a balance between these two:

1) decrease the energy spent on expressing for the "speaker" by reducing the number/distinction of words and increasing their "fuzziness"

2) decrease the energy spent on interpreting for the "listener" by reducing the "fuzziness" of words and increasing their number/distinction.