noun

1. Philos. the ethical doctrine that pleasure, variously conceived of in terms of happiness of the individual or of society, is the principal good and the proper aim of action
2. Psychol. the theory that a person always acts in such a way as to seek pleasure and avoid pain
3. the self-indulgent pursuit of pleasure as a way of life

Etymology: < Gr hēdonē, pleasure (see hedonic) + -ism