Good point. Joke would work.
Also note that plaisanterie can mean playing around, for example "arrêtez vos plaisanteries" translates to "stop joking around" or "stop playing around". So, ceases to be word-play is not that far-fetched.
Witticism, which to me has more of a sense of "a clever joke" (as opposed to just a joke), may be a good word in this context.
Also, you can see if one of these two fits as well: "a clever joke" or "a play on words".