Definition from Wiktionary, the free dictionary
From Latin membrāna (“skin of body”).
membrane (plural membranes)
- A flexible enclosing or separating tissue forming a plane or film and separating two environments (usually in a plant or animal).
- A mechanical, thin, flat flexible part that can deform or vibrate when excited by an external force.
- A flexible or semi-flexible covering or waterproofing whose primary function is to exclude water.
Derived terms 
membrane f (plural membranes)
- Plural form of membrana