ETYM Latin erraticus, from errare to wander: cf. French erratique. Related to Err.
In geology, a displaced rock that has been transported by a glacier or some other natural force to a site of different geological composition.
1. Having no fixed course; SYN. planetary, wandering.
2. Liable to sudden unpredictable change; SYN. fickle, mercurial, quicksilver.
3. Likely to perform unpredictably; SYN. temperamental.

One that is erratic; especially; an erratic boulder or block of rock.