- coquinaAny of several small marine clams, of the species Donax variabilis, common in United States coastal waters.
- conchoidAny of a family of curves defined as the locus of points p, such that each p is on a line that passes through a given fixed point P and intersects a given curve, C, and the distance from p to the point of intersection with C is a specified constant (note that for nontrivial cases two such points p satisfy the criteria, and the resultant curve has two parts).
- cuncaA traditional Galician unit of dry measure, equivalent to about 1–1.5 L depending on the substance measured.