Epicureanism is a hedonism, but an austere one. The 'eat, drink and be merry' caricature actually describes the rival Cyrenaics, who prioritised immediate bodily pleasure — and whom Epicurus argued against. Two versions of one thesis, pointing in opposite practical directions.
Side by side
Aspect
Hedonism
Epicureanism
Is
A family of theses
One member of it
Scope
Value and motivation
A way of living
Ceiling
Unspecified
Painlessness
Caricature fits
The Cyrenaics
Nobody
What each one means
Hedonism
Hedonism names three different things: the value claim that pleasure is the only thing good in itself and pain the only thing bad in itself; the separate psychological claim that pleasure and pain are all that motivate us; and, in everyday use, devotion to pleasure as a way of life.
Epicureanism is Epicurus's teaching that the good life is a quiet one — freedom from bodily pain and mental disturbance, reached by wanting less. In ordinary English the word also means devotion to refined pleasure, especially good food and drink — close to the opposite of what he taught.