1
: having no fixed course : wandering
an erratic comet
2
3
: transported from an original resting place especially by a glacier
an erratic boulder
4
archaic
: nomadic
: one that is erratic (see erratic entry 1)
especially
: a boulder or block of rock transported from its original resting place especially by a glacier
Did you know?
Erratic can refer to literal "wandering". A missile that loses its guidance system may follow an erratic path, and a river with lots of twists and bends is said to have an erratic course. Erratic can also mean "inconsistent" or "irregular". So a stock market that often changes direction is said to be acting erratically; an erratic heartbeat can be cause for concern; and if your car idles erratically it may mean that something's wrong with the spark-plug wiring.
Examples of erratic in a Sentence
Adjective
My sinker has been my most erratic pitch. And when your foundation pitch is lacking, you have to go to other pitches. My sinker has been in and out, but mostly out.
—
Orel Hershiser, in New York Times, 9 May 1999
In winning his two-month match in Yugoslavia against Boris Spassky, 10 games to five, Bobby Fischer was erratic, which was hardly surprising considering his two-decade layoff, but there were times when he played more brilliantly than anybody could have expected.
—Sports Illustrated, 16 Nov. 1992
Over the centuries, in erratic ways, men have constructed a world in which they are relatively free of many kinds of threatening or harmful stimuli …
—B. F. Skinner, Beyond Freedom and Dignity, (1971) 1972
so far your effort to land a summer job has been very erratic
because of your erratic attendance at practice, you're in danger of being cut from the team
Orel Hershiser, in New York Times, 9 May 1999
In winning his two-month match in Yugoslavia against Boris Spassky, 10 games to five, Bobby Fischer was erratic, which was hardly surprising considering his two-decade layoff, but there were times when he played more brilliantly than anybody could have expected.
—Sports Illustrated, 16 Nov. 1992
Over the centuries, in erratic ways, men have constructed a world in which they are relatively free of many kinds of threatening or harmful stimuli …
—B. F. Skinner, Beyond Freedom and Dignity, (1971) 1972
so far your effort to land a summer job has been very erratic
because of your erratic attendance at practice, you're in danger of being cut from the team
Recent Examples on the Web
David Ehrlich, IndieWire, 29 Oct. 2025
After the second hanging, the town doctor cut Hooch’s head off, apparently looking for signs of syphilis (brain involvement is often an indicator), which might seem to explain his erratic behavior.
—Graham Averill, Outside, 28 Oct. 2025
Jeanine Barone, Forbes, 5 Mar. 2025
Car-sized erratics embedded in ice were carried both within the lake area and as much as 500 miles from the lake by flood waters—some of the erratics weighed up to eight and a half tons.
—Keely Larson, Ars Technica, 4 Jan. 2023
See All Example Sentences for erratic
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Adjective
The plot unfolds at the urgent but erratic pace of a life-altering business deal, as Bonitzer unfussily steers us through a series of small rooms as people scramble to determine the proper thing to do with Schiele’s painting.
—David Ehrlich, IndieWire, 29 Oct. 2025
After the second hanging, the town doctor cut Hooch’s head off, apparently looking for signs of syphilis (brain involvement is often an indicator), which might seem to explain his erratic behavior.
—Graham Averill, Outside, 28 Oct. 2025
Noun
Huge boulders — referred to as glacial erratics that were carried by glaciers during the last Ice Age — dot the landscape that’s forested with red maple, spruce and Canadian hemlock.
—Jeanine Barone, Forbes, 5 Mar. 2025
Car-sized erratics embedded in ice were carried both within the lake area and as much as 500 miles from the lake by flood waters—some of the erratics weighed up to eight and a half tons.
—Keely Larson, Ars Technica, 4 Jan. 2023
See All Example Sentences for erratic
Cite this Entry
“Erratic.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/erratic. Accessed 31 Oct. 2025.
Copy CitationMedical Definition
erratic
adjective
er·rat·ic
ir-ˈat-ik 
1
: characterized by lack of consistency, regularity, or uniformity
an erratic pulse
2
: deviating from what is ordinary or standard
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