lanthanum Lanthanotus • lanthopine · · · Info · Definitions · Synonyms · Characters · · lanthanum · · Text Latin · · Script 9 · · Length Definitions · · · (noun) a white soft metallic element that tarnishes readily; occurs in rare earth minerals and is usually classified as a rare earth. Synonyms: La, atomic number 57. · · Noun Definition 1 Synonyms · · · la · · Synonym 1 atomic number 57 · · Synonym 2 Characters · · a latin small letter a U+0061 h latin small letter h U+0068 l latin small letter l U+006C m latin small letter m U+006D n latin small letter n U+006E t latin small letter t U+0074 u latin small letter u U+0075