(anatomy) A membrane which secretes mucus. It forms the lining of various body passages that communicate with the air, such as the respiratory, genitourinary, and alimentary tracts including the mouth, nasal passages, vagina and urethra.

A transparent protective fold of skin acting as an inner eyelid in birds, reptiles and some mammals.

(cytology) The semipermeable membrane that surrounds the cytoplasm of a cell.

(physics, chemistry) a separation method in which a nonwetting, microporous membrane is used with a liquid feed phase on one side of the membrane and a condensing, permeate phase on the other

(chemistry, physics) any of several processes for separating the components of mixtures by using thin barriers between two miscible fluids; any transmembrane force leads to preferential transport of one or more feed components

Alternate spelling of nictitating membrane.

(anatomy) The mucous membrane that lines the nasal chambers; the pituitary membrane.

(anatomy) A layer of rod cells and cone cells in the retina of the human eye.

(humorous, slang, sometimes derogatory) insane; crazy

(biochemistry) A protein that is associated with a biological membrane; association typically refers to either the ability to copurify membrane lipids with said protein or the ability to visualize a physical association in situ.