adjective

not even or regular in pattern or movement; unpredictable.

her breathing was erratic

unpredictable,inconsistent,changeable,variable,inconstant,uncertain,irregular,unstable,turbulent,unsteady,unsettled,unreliable,undependable,changing,ever-changing,volatile,varying,shifting,fluctuating,fluid,mutable,protean,fitful,wavering,full of ups and downs,peaky,mercurial,capricious,whimsical,fickle,flighty,giddy,impulsive,wayward,temperamental,highly strung,excitable,moody,blowing hot and cold,labile,fluctuant,changeful

noun

a rock or boulder that differs from the surrounding rock and is believed to have been brought from a distance by glacial action.

the source of stone for the whetstones may have been glacial erratics