This is the 413th most frequent Catalan word.
santa
The Catalan word "santa" means "saint" (feminine) or "holy" (feminine).
In this case, 'santa' metaphorically describes someone exceedingly kind or virtuous.
És una santa que sempre ajuda tothom.
She is a saint who always helps everyone.
In this religious context, 'santa' is used as an adjective meaning 'holy' or 'sacred' to describe a night.
La nit de Nadal és una nit santa.
Christmas Eve is a holy night.
Here, 'Santa' is part of a proper noun, referring to a saint in honorific usage.