erratic in WordNet English dictionary

1. 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"
   erratic  fickle  mercurial  quicksilver 
   
2. 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
   erratic  temperamental 
   
3. having no fixed course
   "an erratic comet"; "his life followed a wandering course"; "a planetary vagabond"
   erratic  planetary  wandering