What does err mean?
To err is to make a mistake — to be wrong in judgment, action, or fact. It is one of English's oldest verbs of error, carrying a slightly formal tone that suits careful writing: audits, courts, and moral argument. Its most familiar modern home is the phrase 'to err on the side of caution,' which advises choosing the safer path when outcomes are uncertain. The word also survives in the ancient proverb 'to err is human,' a reminder that mistakes are an unavoidable part of being human. Though less common in everyday conversation than 'make a mistake,' err remains valuable for its precision and dignity; it names failure without blame or drama, acknowledging simply that a person or process has gone wrong. Related words such as 'error,' 'erratic,' and 'aberration' all descend from the same Latin root meaning to wander.
To make a mistake or be incorrect.
"The referee erred in awarding the penalty."
Always intransitive in standard English; one errs *in* something or *on the side of* something, never errors something directly.
In the phrase 'err on the side of,' to adopt the more cautious or conservative option among alternatives.
"If you're unsure whether to include the disclaimer, err on the side of including it."
"To err is human" comes from an ancient Roman proverb — but the word itself simply means to wander off course, which is exactly what a mistake is.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of err
Err comes from the Latin verb 'errare,' meaning to wander, stray, or go astray, which entered Middle English via Old French in the medieval period. The underlying image is of wandering off the correct path — a mistake as a form of straying rather than deliberate wrongdoing. From the same root come 'error,' 'errant' (as in knight-errant, literally a wandering knight), 'erratic,' and 'aberration,' all preserving the sense of deviation from what is right or expected.
Related word forms
How err is actually used
Formal to neutral in register; far more common in writing than casual speech, where 'make a mistake' dominates. The fixed phrase 'err on the side of caution' is the most frequent context in modern use. The past tense is regular ('erred'), though some speakers hesitate over it.
Easily confused with err
'Heir' is a noun meaning a person who inherits property or a title, while 'err' is a verb meaning to make a mistake — they sound alike but share nothing in meaning.