didymium
Concise Oxford English Dictionary © 2008 Oxford University Press:
didymium /dɪˈdɪmɪəm/
▶noun Chemistry a mixture containing the rare-earth elements praseodymium and neodymium, used to colour glass for optical filters.
– origin C19: from Gk didumos ‘twin’ + -ium.
'didymium' also found in these Oxford entries:

