Yes, certain words have multiple meanings. We've covered the reason to define which meaning you are using if you think those you are communicating with will be befuddled. That's one reason to define what you are saying.
The other is when you are creating new words. And let's face it - we do that more of-ten than you'd think. When we wrote about using words your audience doesn't know it was because we were pointing out you didn't know either.
If you find yourself in a place where you are using words that others don't know - look up those words to see if someone has given them a definition. Look it up online and find a consistent meaning. If you can't readily find a definition for the term, then define it! Where do you think dictionary definitions come from? You. Me. Them. Everybody! (Everybody, needs somebody! Everybody - needs somebody to define! he laughingly sings...)
Dictionaries are historical references
There. I said it. But more importantly, so did John Simpson, former Chief Editor of the Oxford English Dictionary. Here's a passage (edited for clarity) from a book he recently wrote10:
"It is easy to be too precipitate in selecting a word for inclusion in the dictionary… In general, we learned to shy away from trying to define any new word-wherever possible-until it had a chance to settle down in the language...it is helpful for us to see whether others publish preliminary accounts of the word from their own impressions or research. That's not cheating; it's just good research sense."
The simple point is this - if you want to use a term you can't find a definition for, you need to write that definition. And the great part is, if it is your word, your definition can't be wrong! These types of definitions are called Stipulative definitions, and we'll cover them in a bit.