re·gu·lus 
(rĕgyə-ləs)
(rĕgyə-ləs)n. pl. reg·u·li (-lī) or reg·u·lus·es
1. The metallic mass that sinks to the bottom of a furnace or crucible during smelting.
2. A relatively impure intermediate product of various ores in smelting.
[Latin rēgulus, diminutive of rēx, rēg-, king; see reg- in the Appendix of Indo-European roots.]
regu·line (rĕgyə-lĭn, -līn′) adj.