- (philosophy, not countable) A twentieth-century philosophical movement emphasizing the uniqueness of each human existence in freely making its self-defining choices.
- The heyday of existentialism occurred in the mid-twentieth century.
- (philosophy, countable) The philosophical views of a particular thinker associated with the existentialist movement.
- Sartre's existentialism is atheistic, but the existentialism of Marcel is distinctly Christian.
- 1965, Mikel Dufrenne, "Existentialism and Existentialisms," Philosophy and Phenomenological Research, vol 26 no 1 (Sep), p. 51.
- Instead of Existentialism, we should speak of Existentialisms.