scylla

and charybdis n.pl. Two dangers or extremes such that one can be avoided only by approaching the other. [names of a monster and a whirlpool in greek mythology]

n. A dangerous rock on the Italian coast opposite the whirpool Charybdis on the coast of Sicily, -- both personified in classical literature as ravenous monsters. The passage between them was formerly considered perilous; hence, the saying "Between Scylla and Charybdis," signifying a great peril on either hand.