Straying from the proper course or standard, or outside established limits. / Roving around; wandering. / Prone to making errors; misbehaving.

A knight-errant.

(literary or archaic) A mission or quest. / A mundane mission of no great consequence, concerning household or business affairs (dropping items by, doing paperwork, going to a friend's house, etc.)

(transitive) To send someone on an errand. / (intransitive) To go on an errand.

The process of finding a solution to a problem by trying many possible solutions and learning from mistakes until success is attained.

A mistake made during the process of typing, especially one caused by a slip of the fingers. / A mistake made during the process of typesetting.

(biology) The extinction of an organism (usually microorganisms) due to excessive RNA mutations.

(mathematics) The difference (sometimes defined to be the absolute difference) between the measured or inferred value of a quantity and its true value.

(rare) erratic

(idiomatic) A foolish undertaking, especially one that is purposeless, fruitless, nonsensical, or certain to fail. / (idiomatic) Such an undertaking, assigned as a prank.