Adjective
1. having no fixed course;
"an erratic comet""his life followed a wandering course""a planetary vagabond"2. liable to sudden unpredictable change;
"erratic behavior""fickle weather""mercurial twists of temperament""a quicksilver character, cool and willful at one moment, utterly fragile the next"3. likely to perform unpredictably;
"erratic winds are the bane of a sailor""a temperamental motor; sometimes it would start and sometimes it wouldn't""that beautiful but temperamental instrument the flute"- Osbert Lancaster