not stable; not firm or firmly fixed; unsteady.

liable to fall or sway.

unsteadfast; inconstant; wavering

unstable convictions.

marked by emotional instability

an unstable person.

irregular in movement

an unstable heartbeat.

Chemistry . noting compounds that readily decompose or change into other compounds.

adjective

stable , steady , strong

adjective

ambiguous , borderline , capricious , changeable , dizzy , dubious , erratic , fickle , fitful , fluctuating , giddy , inconsistent , inconstant , insecure , irrational , lubricious , mercurial , mobile , movable , moving , mutable , not fixed , precarious , rickety , risky , rocky , sensitive , shaky , shifty , slippery , suspect , teetering , temperamental , ticklish , tricky , uncertain , unpredictable , unsettled , unsteady , untrustworthy , vacillating , variable , volatile , wavering , weak , weaving , wiggly , wobbly , alterable , fluid , variant , fantastic , fantastical , freakish , whimsical , infirm , tottering , tottery , unsure , astatic , ataxic , eccentric , emotional , flighty , flimsy , fragile , irresolute , labile , loose , protean , shifting , titubant , turbulent , unbalanced , unhinged , unreliable