membrane            
noun [ C or U ]  specialized usuk/ˈmem.breɪn/
 anatomy 膜
a thin piece of skin that covers or connects parts of a person's or animal's body
  The cornea is the transparent membrane that covers the front of the eye. 角膜是覆盖在眼球前部的透明膜。 
  engineering 薄膜;膜状物
a very thin piece of material that covers an opening
  biology 细胞膜
the outer covering of a cell
  a cell membrane 细胞膜