What does erratic mean?
"Erratic" describes something that moves, changes, or behaves in an irregular and unpredictable way, without any consistent pattern. It is commonly applied to people's behaviour, someone's mood or judgment, fluctuating prices or temperatures, and unstable machinery or performance. The word carries a distinctly negative connotation: to call a person's actions erratic suggests unreliability or even instability, which is stronger than simply calling them "varied." The term derives from the Latin errare, "to wander," the same root behind "error" and "errant," and it preserves that image of wandering off course. Interestingly, geologists also use "erratic" as a noun for a boulder carried long distances by a glacier and left stranded in alien terrain — a vividly literal example of the word's core idea. Whether describing a driver swerving between lanes or a heartbeat with an uneven rhythm, "erratic" conveys unpredictability that unsettles or alarms.
Irregular, unpredictable, or inconsistent in movement, behaviour, pattern, or quality.
"His attendance at work became increasingly erratic over the winter."
A rock fragment transported by glacial ice and deposited at a distance from its place of origin, often differing from the local bedrock.
"Geologists identified the boulder as an erratic carried down from the mountains thousands of years ago."
This sense is chiefly technical, used in geology and earth sciences.
Applies only to the geological noun sense, referring to multiple glacially transported rock fragments.
"The field was littered with erratics left behind by the retreating glacier."
Glaciologists still use "erratic" in its original literal sense: massive boulders stranded miles from home by ancient glaciers — rocks that literally wandered off course.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of erratic
"Erratic" comes from the Latin verb errare, meaning "to wander" or "to stray," via the adjective errare-derived errans/errantis, "wandering." English adopted it from French or directly from Latin around the early seventeenth century, first describing things that wander or have no fixed course. It shares this root with "error," "errant," "aberration," and "errand," all of which carry the idea of straying or moving about. The geological sense of a displaced glacial boulder developed later as scientific terminology.
Related word forms
How erratic is actually used
Most often used to describe behaviour, performance, weather, or patterns that swing unpredictably; it frequently carries a mildly negative or worrying connotation. The geological noun sense is technical and largely confined to earth sciences.
Easily confused with erratic
"Erotic" relates to sexual desire, while "erratic" means irregular or unpredictable — they differ by only one letter but are unrelated in meaning.