This is the 624th most frequent Finnish word.
lauantaina
"On Saturday."
In this context, 'lauantaina' indicates the day of the week when the action occurs, specifying it is on Saturday.
Lauantaina menemme kauppaan ostoksille.
On Saturday, we will go shopping.
Here, 'lauantaipäivänä' (constructed from 'lauantaina' and 'päivänä') emphasizes the entire day of Saturday as the time period.
Hän valmistautui kokeeseen koko lauantaipäivänä.
She prepared for the exam throughout Saturday.
Here, 'lauantaina' is used as an adverb to denote the specific day on which the action of going to the store takes place.