My sister and I used to play this when we were kids. Maybe I'll share a few of our other games at another time.
I'm also not sure if a similar game has been done already, but I hope it hasn't.
So, to play the related game, a person says a word, and the next person must say a word related to the previous word in some way. For example, if I say "fish", someone could say "swimming". The next person could say "pool", and so on. The one rule is you CANNOT repeat a word that's already been used. You can use synonyms but not the exact word.
I'll start:
Rabbit