What spice is made from the seeds of the plant whose leaves are called cilantro?

Cumin and cilantro are two different plants that are not the same species. Cumin is the ground up seeds of the plant Cuminum cyminum and cilantro the leaves from Coriandrum sativum.

Also, cilantro (leaves) and coriander (ground up seeds) come from that same species, Coriandrum sativum. Perhaps you were thinking of coiander instead of cumin?