Entry 1 sense Webster, 1913 Preformation · Pre·for·ma·tion · IPA /pɹiːfɔːˈmeɪʃ(ə)n/ 01 n. An old theory of the preëxistence of germs. Cf. Emboîtement. 1. An old theory of the preëxistence of germs. Cf. Emboîtement.(Biol.) See: Emboîtement