indiumPronunciation: /ˈɪndɪəm/Definition of indium noun [mass noun] the chemical element of atomic number 49, a soft silvery-white metal occurring naturally in association with zinc and some other metals. (Symbol: In)Origin: mid 19th century: from indigo (because there are two characteristic indigo lines in its spectrum) + -iumindium in other Oxford dictionaries Definition of indium in the US English dictionary