warn off phrasal verb ( see also ↑ warn )
1 . warn somebody ↔ off to tell people that they should not go near something, especially because it might be dangerous:
Some animals mark their territory to warn off rivals.
2 . warn somebody off (doing) something especially British English to tell someone that they should not do or use something because it might be dangerous:
Doctors should have warned people off using the drug much earlier than they did.