opna

1. (in the body) membrane
   Od jakog udarca pukla mu je bubna opna. — The heavy blow burst his eardrum.
   Upala moždanih opna je opasna bolest. — Inflammation of the meninges is a dangerous disease.
2. film; thin skin
   Ispod ljuske jajeta nalazi se tanka opna. — There's a thin skin under the eggshell.

Bubna opna means 'eardrum'.