This is the 2600th most frequent Polish word.
thomas
The word "thomas" is not a Polish word; it is an English name.
The word 'Thomas' here is used as the name of a person, indicating that the subject of the sentence is the speaker's friend.
Tomasz jest moim przyjacielem.
Thomas is my friend.
In this sentence, the word 'Thomas' is in its genitive (possessive/direct object) case form, as used in Polish when talking about a person's involvement in an event like meeting.
Spotkałem Tomasza wczoraj na ulicy.
I met Thomas on the street yesterday.
Here, 'Thomas' is in another grammatical case, appropriate for the context of discussing or referring to him.