mercurial

Synonyms: blowing hot and cold bubbleheaded buoyant capricious changeable effervescent elastic erratic expansive fickle flaky flip fluctuating gaga gay impulsive inconstant irregular irrepressible lighthearted lively lubricious mad mobile movable quicksilver resilient short-fuse spirited sprightly ticklish unpredictable unstable up-and-down variable volatile yo-yo

Antonyms: calm tranquil unchangeable unperturbable unvarying