A monster of the Lernean marshes, in Argolis. It had nine
heads, and Hercules was sent to kill it. As soon as he struck off one
of its heads, two shot up in its place.
Having as many heads as the hydra (q.v.
); a difficulty which
goes on increasing as it is combated.
The rabble, which not only is many-headed numerically, but seems
to grow more numerous the more it is attacked and resisted.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894