This is the 968th most frequent Polish word.
sierpniu
The word "sierpniu" in Polish means "August" (locative case).
The word 'sierpniu' is the locative form of 'sierpień' and is used here to indicate the time when something occurs, 'in August'.
W sierpniu zwykle mamy wakacje.
In August, we usually have holidays.
The word 'sierpniu' appears as a locative case to denote the period during which the planned action occurs, highlighting 'in August'.
Będziemy w Polsce w sierpniu.
We will be in Poland in August.
'Sierpniu' is in the locative case, used to specify the past context of the subject's actions during 'in August'.