This is the 502nd most frequent Portuguese word.
dia
"Dia" means "day" in English.
In this sentence, 'dia' is used to denote a unit of time, specifically referencing 'day'.
Hoje é um dia lindo.
Today is a beautiful day.
Here, 'dia' is used within a date to specify the day within a month.
Ela nasceu no dia vinte de março.
She was born on the twentieth day of March.
In this context, 'dia' refers to a single complete unit of day as a time frame for an action.