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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.

Choosing depth over volume also matters: one carefully reported long-form article will inform you better than bursts of random, unreliable and emotionally loaded posts on Instagram.

From Science Daily • Jun. 16, 2026

An unnamed Ethiopian assistant professor was selected by ICM for its Midwife Leaders Executive Sponsorship Programme, but was rejected for having an "inadequate financial bank statement and an unreliable purpose of travel", the organisers said.

From Barron's • Jun. 12, 2026

And Mr. Mezrich “would be the first to admit that as a writer, he was perhaps the most unreliable of them all.”

From The Wall Street Journal • Jun. 3, 2026

Mobile data can be unreliable, too - especially when trains travel through tunnels.

From BBC • May 30, 2026

Akhi had become so unreliable that I wasn’t able to depend on him at all.

From "Proud" by Ibtihaj Muhammad

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