invagination

 
Pronunciation: /ɪnˌvadʒɪˈneɪʃ(ə)n/

noun

[mass noun] chiefly Anatomy & Biology
  • the action or process of being turned inside out or folded back on itself to form a cavity or pouch.
  • [count noun] a cavity or pouch so formed.

Origin:

mid 17th century: from modern Latin invaginatio(n-), based on in-2 'into' + Latin vagina 'sheath'