avisar

A common everyday verb meaning to warn, notify, or let someone know in advance — avisar con tiempo, avisar a la policía, avísame cuando llegues. One of the basic verbs of everyday communication in Spanish.

• Avísame cuando llegues a casa. — Let me know when you get home.
• Deberías avisar con más tiempo la próxima vez. — You should give more notice next time.
• Avisaron a los vecinos antes de cortar el agua. — They notified the neighbors before cutting off the water.

Not the same as advertir (to warn of danger) in every context — avisar just means to inform or let someone know, while advertir carries a stronger sense of cautioning against a risk.

Often confused with advertir.

• expression "El que avisa no es traidor" — A widely used Spanish proverb meaning that someone who warns you in advance about a problem or their intentions shouldn't be considered disloyal for it — a fixed saying with its own dedicated entries in Spanish proverb dictionaries and columns.