Thinking, learning and playing - all embodied in one simple book:
... The dictionary, of course.
Each participant in their turn, with their eyes closed, opens the dictionary at a random page, points to a random place on the page, and reads the word out loud. The others, of course, try to guess its meaning. Who wins? Whichever way you choose: the one who guessed closest to the real meaning of the word; offered the most logical sense; or maybe gave an original or funny interpretation to the word. Obviously, you can also play for fun only, without winners... :-)
What would be a "logical" sense of a word we don't know? It might be based on the resemblance of the word to other words; on its structure, etc. Beyond the fun of revealing new words, you may be surprised to find out that some of them become absorbed in memory for long after the game. Additionally, rummaging through a dictionary - same as an encyclopedia - always involves further interesting or funny revelations, thanks to the alphabetic order which places side by side words and concepts from very different contexts. If we're not interested in one, surely we'll find another one interesting.
Did you notice that the grown-ups are learning many new words as well?...