verb
warn
WORN/wɔːrn/
To alert someone to possible danger or trouble.
The hiker warns his companion about the broken bridge board.

Etymology
Old English warnian covered both giving notice of danger and taking heed. The modern sense preserves the first side: alerting people so they can take precautions.
In context
false teaching began to make its way through Timothy's congregation and Paul wrote to warn him about the consequences of compromise
More examples
- She warned them before the storm arrived.
- They have warned visitors to stay clear.
- The sign warns drivers of the sharp bend.
Forms
warn · warns · warned · warning
warning noun — A notice of possible danger or trouble.