a mixture containing two or more metallic elements or metallic and nonmetallic elements usually fused together or dissolving into each other when molten; "brass is an alloy of zinc and copper"
the musical interval between one note and another four notes away from it
following the third position; number four in a countable series
coming next after the third and just before the fifth in position or time or degree or magnitude; "the quaternary period of geologic time extends from the end of the tertiary period to the present"