This is the 2454th most frequent Spanish word.
santo
Holy or saint.
Here, "santo" refers to a holy or canonized person from a religious context.
El día de hoy celebramos el día de todos los santos.
Today we celebrate All Saints' Day.
In this usage, "santo" is metaphorically describing someone as virtuous and exemplary, akin to a saint.
Él es un hombre tan bueno que parece un santo.
He is such a good man that he seems like a saint.
"Santo" here is an adjective describing God, emphasizing sanctity and reverence.