This is the 11739th most frequent German word.
tadej
"Tadej" is not a German word; it is a Slavic male given name, equivalent to Thaddeus in English.
Here, 'Tadej' is used as a proper noun, presumably a person's name.
Tadej ist ein freundlicher Mensch.
Tadej is a friendly person.
In this example, 'Tadej' functions as a proper noun denoting someone who is the subject of the story.
Wir haben eine interessante Geschichte über Tadej gelesen.
We read an interesting story about Tadej.
Here, 'Tadej' is in the genitive case, showing possession, i.e., Tadej owns the suggestion.