It looks like you've taken 'once' from the definition - 'once out of water', (and it does make the riddle read better) but I think it's a crucial indicator that the answer to the clue is archaic.
There isn't an abbreviation in the answer to the riddle for the bottom quadrant - and there isn't an instruction as such. The answer to the 'riddle' is a pun on the b+c words as they relate to this pursuit of ours (it's an in-joke, really) and the one word 'answer' is simply followed from start to finish.