Source : Webster's Revised Unabridged Dictionary (1913)

Regulus \Reg"u*lus\ (-l?s), n.; pl. E. {Reguluses} (-?z), L.
   {Reguli} (-l?). [L., a petty king, prince, dim. of rex,
   regis, a king: cf. F. r['e]gule. See {Regal}.]
   1. A petty king; a ruler of little power or consequence.

   2. (Chem. & Metal.) The button, globule, or mass of metal, in
      a more or less impure state, which forms in the bottom of
      the crucible in smelting and reduction of ores.

   Note: The name was introduced by the alchemists, and applied
         by them in the first instance to antimony. It signifies
         little king; and from the facility with which antimony
         alloyed with gold, these empirical philosophers had
         great hopes that this metal, antimony, would lead them
         to the discovery of the philosopher's stone. --Ure.

   3. (Astron.) A star of the first magnitude in the
      constellation Leo; -- called also the {Lion's Heart}.