This is the 4820th most frequent Polish word.
ojcem
"Ojcem" means "father" in the instrumental case in Polish.
The word 'ojciec' is used in its nominative form here as the subject of the sentence.
Mój ojciec jest lekarzem.
My father is a doctor.
Here, 'ojcem' is in instrumental case, as it appears after the preposition 'z', indicating 'with whom'.
Rozmawiałem z moim ojcem o wakacjach.
I talked to my father about the holidays.
In this sentence, 'ojca' is in genitive case due to the phrase 'z mojego' which requires it to express possession.