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Synonyms

unreliable

American  
[uhn-ri-lahy-uh-buhl] / ˌʌn rɪˈlaɪ ə bəl /

adjective

  1. not reliable; not to be relied or depended on.

    Synonyms:
    untrustworthy, irresponsible, undependable

unreliable British  
/ ˌʌnrɪˈlaɪəbəl /

adjective

  1. not reliable; untrustworthy

    an unreliable witness

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Other Word Forms

Etymology

Origin of unreliable

First recorded in 1830–40; un- 1 + reliable

Explanation

Someone unreliable can't be trusted to do something. Things can be unreliable too, like a bike with a wobbly wheel. The word "rely" is a clue to what unreliable means. When you can rely on something, you can count in it — it's reliable. On the other hand, you'd better not count on an unreliable person. People can be unreliable because they're dishonest, always late, bad at their job, or just inconsistent. Things can be unreliable because they're broken or old. A train schedule can be unreliable if the trains are never on time. Unfortunately, there's a lot of stuff in life that's unreliable, so be careful.

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Vocabulary lists containing unreliable

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

See Examples For:

Critics of Pangram and other AI-detectors say they are unreliable – with different programmes often giving different results after analysing the same texts.

From BBC ● Sep. 23, 2026

Large-scale water treatment technology remains known and used, but supply lines for chemicals and spare parts are unreliable.

From Science Daily ● Sep. 22, 2026

But the Fed’s use of interest rates to steer the economy and labor markets can be unreliable.

From The Wall Street Journal ● Sep. 14, 2026

Any halfway decent lawyer knows that polygraphs are so unreliable that the results are inadmissible in court.

From Salon ● Sep. 14, 2026

Before the Scientific Revolution facts were few and far between: they were handmade, bespoke rather than mass produced, they were poorly distributed, they were often unreliable.

From "The Invention of Science" by David Wootton

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