Merriam-Webster Collegiate Dictionary - concha

 I. noun  (plural ~e)  Etymology: Italian & Latin; Italian conca semidome, apse, from Late Latin ~, from Latin, shell  Date: circa 1639  1.  a. the plain semidome of an apse  b. apse  2. something shaped like a shell; especially the largest and deepest concavity of the external ear  • ~l adjective  II. noun  also concho  Etymology: American Spanish ~, from Spanish, shell, from Late Latin conchula, diminutive of Latin ~  Date: 1887 an ornamental disk (as on clothing or tack) of American Indian origin featuring a shell or flower design