quick ‧ sil ‧ ver /ˈkwɪkˌsɪlvə $ -ər/ BrE AmE noun [uncountable]
1 . old use the metal ↑ mercury
2 . literary something that is like quicksilver changes or moves quickly in a way that you do not expect:
His mood changed like quicksilver.
—quicksilver adjective :
his quicksilver temperament