This is the 430th most frequent Polish word.
nami
"With us."
Here, "nami" is the instrumental form of "my" (we) and is used to indicate accompaniment in the phrase "z nami" (with us).
Chodź z nami na spacer.
Come with us for a walk.
The use of "nami" here in "z nami" (with us) again employs the instrumental case to express accompaniment, specifically in the context of meeting or gathering.
Spotkasz się z nami w kawiarni?
Will you meet with us at the café?
In this instance, "nami" in "z nami" (with us) shows the instrumental case to relate to the idea of being involved together or associated.