What does unreliability mean?
Unreliability is the noun meaning the quality of not being dependable, consistent, or predictable. It describes both general tendencies and specific failures: a person may show unreliability by missing commitments or behaving inconsistently, while a machine, transport system, or data source may be unreliable because it fails, varies unexpectedly, or produces inconsistent results. The word is often formal and carries a negative connotation, suggesting that trust, stability, or practical performance cannot safely be assumed. It is especially useful in discussions of technology, infrastructure, research, public services, and interpersonal conduct. Rather than merely saying that something is bad, unreliability identifies the specific problem of inconsistency or failure to perform as expected. This makes it a useful term for analyzing why people cannot plan around a service, why an experiment yields erratic results, or why a relationship may feel unsafe.
nounThe quality of being unreliable; the condition of failing to work consistently or of not being dependable. It refers to a lack of reliability, stability, or trustworthiness.
- The quality or condition of being unreliable; lack of dependability, consistency, or predictability.
"The constant unreliability of the train service made it difficult for commuters to plan their journeys."
"The report cited the unreliability of the sensors as the main cause of the false alarms."
"His growing unreliability made the team question whether he could be trusted to meet the deadline."
The plural is uncommon; most speakers use the noun in the uncountable singular form.
"The report documented several unreliabilities in the network."
When promises, machines, and systems cannot be counted on, their problem has a name: unreliability.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does unreliability come from?
Unreliability is an English noun formed from the adjective unreliable, which combines the prefix un- with reliable. Reliable itself was formed from rely with the suffix -able, expressing the ability to be trusted or depended upon. The formation unreliability follows the standard English pattern of converting an adjective into a noun with the suffix -ity. Related words such as reliance and reliant belong to the same English lexical family.
How unreliability is actually used
This is a formal noun, especially common in technical, institutional, and social contexts. It is generally used as an uncountable noun; the plural is uncommon.
Easily confused with unreliability
Reliability is the quality of being dependable or consistent, whereas unreliability is the absence or reduction of that quality.