Here's a breakdown of the word:
* Manhã: This means "morning" in Portuguese.
* -inha: This is a diminutive suffix, similar to "-ie" or "-y" in English, used to make words sound smaller or cuter.
So, "maninha" literally means "little morning," but it's used as a pet name for a younger sister, similar to "sis" or "lil' sis" in English.