The Mahometans say that the eating of a melon produces a
thousand good works. So named from Melos.
Etre un melon.
To be stupid or dull of comprehension. The melon-pumpkin or squash
is soft and without heart, hence “être un melon” is to be as
soft as a squash. So also “avoir un &cocur; de melon” (or de
citrouille) means to have no heart at all. Tertullian says of
Marcion, the heresiarch, “he has a pumpkin
[peponem ] in the place of a heart [cordis loco ].” It
will be remembered that Thersites, the railer, calls the Greeks
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894