vikunni

In a sentence

• Ég áætla að fara í sund í vikunni.

  I plan to go swimming during the week.

  The word 'vikunni' is used here as the locative case of 'vika' (week), indicating the time period in which the action will occur.

• Við höfum mikið að gera í lok vikunnar.

  We have a lot to do at the end of the week.

  The word 'vikunni' functions as the locative form to specify the exact timing within the week, i.e., at its end.

• Þetta verkefni þarf að ljúka í vikunni.

  This task must be completed within the week.

  Here, 'vikunni' points to the duration in which the task is to be completed, implying sometime during the week.