1. [ adjective ] liable to sudden unpredictable change
Synonyms: erratic mercurial fickle

"erratic behavior" "fickle weather" "mercurial twists of temperament" "a quicksilver character, cool and willful at one moment, utterly fragile the next"

Related terms: changeable
2. [ noun ] (chemistry) a heavy silvery toxic univalent and bivalent metallic element; the only metal that is liquid at ordinary temperatures
Synonyms: mercury hydrargyrum atomic_number_80 Hg
Related terms: metallic_element calomel cinnabar