Template:Wikt Editor-In-Chief: C. Michael Gibson, M.S., M.D. 
A commissure is the place where two things are joined. The term is used especially in the fields of anatomy and biology.
In anatomy, commissure can refer to a number of such bodily junctions. The most common usage of the term refers to the brain's commissures, of which there are two—the anterior and posterior—and which consist of fibre tracts that connect the two cerebral hemispheres and span the longitudinal fissure. The term may also refer to the junction of the upper and lower lips, or of the upper and lower eyelids.
In biology, the meeting of the two valves of a brachiopod or clam is a commissure; and in botany, when a fern's laterally expanded vein endings come together in a continuous marginal sorus.