Entry 1 sense Webster, 1913 Gastrulation /(găs`trụ*lā"shŭn)/ · Gas·tru·la·tion · IPA /ɡˌæstrəlˈeɪʃən/ 01 n. The process of invagination, in embryonic development, by which a gastrula is formed. 1. The process of invagination, in embryonic development, by which a gastrula is formed.(Biol.)