Merriam-Webster Collegiate Dictionary - pellicle

 noun  Etymology: Middle French pellicule, from Medieval Latin pellicula, from Latin, diminutive of pellis  Date: 1541 a thin skin or film: as  a. an outer membrane of some protozoans (as euglenoids or paramecia)  b. a film that reflects a part of the light falling upon it and transmits the rest and that is used for dividing a beam of light (as in a photographic device)