verb, particle · to advise or inform someone of a potential danger, harm, or negative consequence

医生警告他，如果不戒烟身体会出问题。

verb · to issue a formal disciplinary warning or official reprimand regarding behavior

他因为违反公司规定受到了书面警告。

verb · a noun referring to a notice or statement that tells someone about a possible danger or problem; a caution.

这不是警告。