1. (

• erratic ,
• fickle ,
• mercurial ,
• quicksilver

) 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" ;

2. (

• erratic ,
• planetary ,
• wandering ,

) having no fixed course; "an erratic comet"; "his life followed a wandering course"; "a planetary vagabond" ;

3. (

• erratic ,
• temperamental

) 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 ;