Example : Erratic behavior.
Fickle weather.
Mercurial twists of temperament.
A quicksilver character, cool and willful at one moment, utterly fragile the next.

Synonyms : fickle, mercurial, quicksilver

Example : An erratic comet.
His life followed a wandering course.
A planetary vagabond.

Synonyms : planetary, wandering

Example : 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.

Synonyms : temperamental