warn

warn /ˈwoɚn/ verb
warns; warned; warning
warn
/ˈwoɚn/
verb
warns; warned; warning
Britannica Dictionary definition of WARN
1 
: to tell (someone) about possible danger or trouble
[+ object]
[no object]
— usually + about or of
2 
: to tell (someone) to do or not to do something in order to avoid danger or trouble
[+ object]
[no object]
— usually + against

warn off

[phrasal verb]
warn (someone) off or warn (someone) off (something)
: to tell (someone) to go or stay away in order to avoid danger or trouble