This is the 7188th most frequent Polish word.
jamesem
"Jamesem" is the instrumental case of the name "James" in Polish.
The word 'Jamesem' here is the instrumental case of the proper noun 'James', used to indicate accompaniment.
Spotkałem się wczoraj z Jamesem na kawie.
I met with James yesterday over coffee.
In this sentence, 'Jamesem' is again in the instrumental case, specifying the person who was involved in collaboration.
Ona pracowała nad projektem razem z Jamesem.
She worked on the project together with James.
The word 'Jamesem' in this example serves the same grammatical function as the instrumental case, denoting the person spoken to.