This is the 189th most frequent Czech word.
sobotu
"Saturday" (accusative form of "sobota").
Here, 'sobotu' is in the accusative case, used as an adverbial of time to specify when an action happens.
V sobotu jdeme na výlet.
On Saturday, we are going on a trip.
In this sentence, 'sobotu' is used again in the accusative case alongside 'každou' for habitual actions occurring on Saturdays.
Každou sobotu chodíme nakupovat.
Every Saturday, we go shopping.
The word 'sobota' here is in the nominative case, as it acts as the subject of the sentence referring to the day.