What does fault mean?
Fault is a versatile English noun with two principal everyday meanings: blame or responsibility for something gone wrong, and a defect or imperfection in a person, thing, or process. When we say an accident was someone's fault, we assign them culpability; when we speak of a fault in a machine or argument, we identify a flaw needing correction. A third, specialized sense belongs to geology, where a fault is a fracture in the Earth's crust along which rock masses have moved — the mechanism behind most earthquakes. The word appears in many fixed expressions, including 'find fault with,' meaning to criticize habitually, and 'to a fault,' describing a virtue carried to excess. Its derivatives include 'faulty' (defective) and 'faultless' (without flaw). Derived ultimately from Latin through Old French, fault entered English via legal usage, where it still carries weight in questions of negligence and liability. Its blend of moral, practical, and scientific registers makes it a small word with remarkable reach.
Responsibility or blame for a mistake, offense, or failure; alternatively, a defect or imperfection in something; in geology, a fracture in rock along which displacement has occurred.
"The power outage was traced to a fault in the transformer."
The plural 'faults' is standard across all senses.
(chiefly British) To find fault with; to criticize.
"No one could fault her commitment to the project."
Regular pluralization applies across all senses: personal faults, mechanical faults, geological faults.
"The inspection revealed several faults in the building's electrical system."
In geology, the faults in California's crust are why San Francisco and Los Angeles are slowly sliding past each other — and why 'the San Andreas Fault' is one of the only faults most people can name.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of fault
Fault derives from Old French 'faute', itself from Vulgar Latin *fallita, rooted in Latin 'fallere', meaning to deceive or fail. It entered English in the Middle Ages, initially in legal contexts concerning lapses or errors. The same Latin root produced English words such as 'fail', 'false' (via 'falsus'), and 'default', making fault part of a large family of words connected to deception and failure. The geological sense developed later, from the general sense of a defect or break.
Related word forms
How fault is actually used
As a noun, fault carries strongly negative connotations when used of blame, but is comparatively neutral when describing minor defects ('a fault in the wiring'). The phrase 'to a fault' idiomatically describes a positive quality carried to excess, as in 'generous to a fault.' The verb form, chiefly British, means to find fault with or criticize.
Easily confused with fault
Default means failing to fulfill an obligation or a preselected setting, while fault means blame or an imperfection — they share Latin roots but have entirely different meanings.