patch

small circumscribed area differing in color or structure from the surrounding surface. her'ald p., the initial manifestation of pityriasis rose a, consisting of a large, solitary, oval patch of efflorescence preceding sometimes by several days the general eruption, mu'cous one of a group of round or oval grayish yellow macerated papules or macules, occurring on the mucous membrane of the mouth or other orifices in syphilis, o'paline p., a mucous p. of silver gray appearance.