phrase/poˌneɾ los ˈkweɾnos/
to cheat on, put horns on
“Se puso furioso cuando descubrió que su mujer le estaba poniendo los cuernos.” — He was furious when he found out his wife was cheating on him.
Synonyms: poner el gorro, gorrear
Already attested in the 13th century, as Old Spanish poner las cuernas, which, however, had the different meaning “to turn (someone) into a cuckold”.