amorphous set
infinite set which is not the disjoint union of two infinite subsets (in models of set theory in which the axiom of choice fails)
en-GB/əˈmɔːfəs ˈsɛt/
en-US/əˈmɔɹfəs ˈsɛt/
infinite set which is not the disjoint union of two infinite subsets (in models of set theory in which the axiom of choice fails)