adjective
Definition: Not consistent or regular; unpredictable in behavior or performance.
Example: The weather has been erratic lately, changing from sunny to rainy in just a few minutes.
noun
Definition: A large rock that has been moved from its original location, often by a glacier, or a person or thing that behaves in an unpredictable or inconsistent way.
Example: The erratic boulder stood alone in the field, a reminder of the glacier's past movement.