[ch=k]. A whirlpool on the coast of Sicily. Scylla and Charybdis are employed to signify two equal dangers. Thus Horace says an author trying to avoid Scylla, drifts into Charybdis, i.e. seeking to avoid one fault, falls into another. The tale is that Charybdis stole the oxen of Hercules, was killed by lightning, and changed into the gulf.
“Thus when I shun Scylla, your father, I fall into Charybdis, your mother.” —Shakespeare: Merchant of Venice, iii. 5.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894