A: Let’s start with some of the things that will probably not be contentious.

• Plurals of a noun definitely count as saying that word. If I ban the word “card” and someone says “cards” most would agree that person must take the penalty.

• Homophones, words spelled differently but pronounced the same definitely don’t count as saying the word (to, too; hear, here; bare, bear). Someone might raise the issue upon hearing a homophone, but the completely different spelling AND meaning would probably be enough to get them to drop it.

• Homographs, words spelled the same but pronounced differently and having a different meaning, probably won’t even come up. Everyone is listening for the word in question, not watching for it in a transcript. Like if someone designates “bow,” a thing you shoot, and someone says “bow,” to bend down, nobody’s going to call that out.

HOWEVER… once you start to get into words that are spelled the same AND sound the same… things get more nebulous.

If I forbid the word “play” then everyone is probably on board as including both the following noun and verb:
noun: the action you take in the game, and its plural. “How many plays do I have left in this turn?”
verb: to take that action, and its various tenses and conjugations. “Play your cards already!” “Have you played yet?” and, “If he plays that card, I’m screwed.”
Or even the adjective designating a type of card. “Did someone change the Play rule while I was out of the room?”

But what about saying you went to a play last night? What about saying your kid plays the clarinet?

If I forbid the word “mean” which one do I… ahem… mean? Is it a verb: to intend? Is it an adjective: cruel? Is it a noun, the average? Our ears probably want to “catch” someone else using all of these, so what do we do?

The safest thing to do is to raise or point out this technical aspect when designating the forbidden word, so that everyone knows what to expect. Discuss it while holding the card up, perhaps, and say that when the card is placed on the table, the ban goes into effect, making sure everyone hears, understands, and agrees.

Here’s a good page describing homophones, homographs, and homonyms.