What does afoul mean?
Afoul is an adverb meaning into a state of conflict, entanglement, or difficulty. In modern English it is almost entirely confined to two idiomatic phrases: 'run afoul of' and 'fall afoul of', both of which mean to come into collision or disfavour with a person, law, institution, or situation. A politician might run afoul of ethics rules; a business might fall afoul of safety regulations. The word originated as a nautical term describing ships that had literally fouled one another — their rigging or hulls tangled in collision — before extending figuratively to any kind of trouble. Because it is bound so tightly to its two phrases, afoul functions less like a free-standing adverb and more like part of a fixed expression. It carries an unmistakably negative connotation and is most at home in formal, legal, and journalistic writing, where it concisely signals that someone has crossed a line or landed in serious difficulty.
Into conflict, difficulty, or entanglement with someone or something; used chiefly in the phrases 'run afoul of' and 'fall afoul of'.
"The startup ran afoul of antitrust regulators within a year of launching."
Almost exclusively found in the fixed phrases 'run afoul of' and 'fall afoul of'; rarely used independently.
In a state of collision or tangling with another vessel or object, especially with rigging or hulls fouled together.
"The two schooners came afoul of each other in the fog."
This literal maritime sense is now largely historical but was the original meaning of the word.
Despite being centuries old, 'afoul' survives today almost solely inside two fixed phrases — you'll rarely meet it anywhere except running or falling afoul of something.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of afoul
Afoul derives from the prefix 'a-' (from Old English 'on', meaning 'in' or 'into') combined with 'foul', from Old English 'fūl', meaning filthy, corrupt, or wicked. It emerged as a nautical term in the 17th century, describing vessels whose rigging or hulls had become tangled or fouled through contact. From this literal maritime sense it extended figuratively to mean getting into trouble or conflict with anything — laws, authorities, or circumstances — a usage that remains dominant today. Its root connects it to other words of Old English origin such as 'filth' and derivatives like 'befoul' and 'defile'.
How afoul is actually used
Afoul is virtually never used outside the phrases 'run afoul of' and 'fall afoul of'. It carries a negative connotation and appears most often in legal, journalistic, and formal contexts. The nautical sense — literally fouling another ship's rigging or hull — is now largely historical but explains the word's figurative extension to trouble generally.
Easily confused with afoul
'Afoot' means in progress or underway, while 'afoul' means in conflict or entanglement with something.