you already said it's not caesium, but I'm guessing it's a derivative word of that... caeside or caesite or something, but I don't know any (nor enough chemistry to generate them)
other than that (and 77) I can't think of anything.
Looking at the game above, DJ defended CONSTRICT, which was eventually guessed. What would have happened if he had defended CONST and someone gave a clue for CONSTRICT since the defended word is a prefix of the guessed word?