Can you give a few examples where it's undefined or ambiguous? I've never noticed a need for more formal definitions than given in a dictionary (for human use) or textbook (for various technical domains). Note that it DOES mean slightly different things in different topics. This is true for a LOT of words.
We know that these words can be objectively defined based on physics. So why don't we have a recognised formal definition? And a Wikipedia article with such a definition?