gadolinium Syllabification: (gad·o·lin·i·um)Pronunciation: /ˌgadlˈinēəm/Definition of gadolinium noun the chemical element of atomic number 64, a soft silvery-white metal of the lanthanide series. (Symbol: Gd)Origin: late 19th century: from gadolinitegadolinium in other Oxford dictionaries Definition of gadolinium in the British & World English dictionary