spec·u·lum  an instrument that exposes the interior of a passage or cavity of the body by enlarging the opening. Nasal Speculum bivalve speculum, one with two blades that are adjustable. Cook speculum, a three-pronged rectal speculum. duck-billed speculum, a type of bivalve vaginal speculum. eye speculum, an appliance for keeping the eyelids apart. Eye Speculum Graves speculum, a type of two-valved vaginal speculum. Kelly speculum, a tubular rectal speculum fitted with an obturator; called also Kelly sphincteroscope. Martin speculum, a rectal speculum consisting of a conical cylinder with an obturator. rectal speculum, one that enlarges the diameter of the rectum for an examination. Sims speculum, a double duck-billed vaginal speculum. stop speculum, an eye speculum with an appliance for controlling the degree to which its branches spread. vaginal speculum, one that enlarges the vaginal opening for use in a vaginal examination.   tri·valve  having three valves or three blades, as a speculum.