castor and pollux

from The Century Dictionary.

• noun In astronomy, the constellation of the Twins, or Gemini, and also the zodiacal sign named from that constellation, although the latter has moved completely out of the former.
• noun An ancient classical name of the corposant, or St. Elmo's fire.
• noun [lowercase] The name given to two minerals found together in granite in the island of Elba. See the separate names.

from the GNU version of the Collaborative International Dictionary of English.

• (Naut.) See Saint Elmo's fire, under saint.