警告 (jǐng gào) means to warn someone seriously, often about official rules or potential danger, with an implied threat of consequences. It is stronger and more directive than 提醒 (tí xǐng 'to remind'), which is a softer nudge. Compared with 告诫 (gào jiè 'to admonish'), 警告 is more direct and urgent, while 告诫 carries a tone of moral advice.