membrane

1. A mechanical, thin, flat flexible part that can deform or vibrate when excited by an external force. (countable, uncountable)
2. A flexible or semiflexible covering or waterproofing whose primary function is to exclude water. (countable, uncountable)
3. A microscopic double layer of lipids and proteins forming the boundary of cells or organelles. (countable, uncountable)
4. A piece of parchment forming part of a roll. (countable, uncountable)

Plural membranes