This is the 15677th most frequent Polish word.
synom
The Polish word "synom" doesn't exist; it may be an error or typo. If you meant "synom" as in "synonim," it means "synonym" in English.
Syn is used here to indicate a direct noun in nominative case as the subject of the sentence, referring to someone's male child.
Mój syn jest bardzo utalentowany w grze na pianinie.
My son is very talented at playing the piano.
Synem (inflected form of syn) is in instrumental case, used after the preposition z specifying whom I need to talk more with.
Wiem, że muszę rozmawiać więcej z moim synem.
I know I need to talk more with my son.
Syna (inflected form of syn) is in accusative case, indicating the direct object of the verb widziałem.