This is the 1168th most frequent Polish word.
wiedzą
"Wiedzą" means "they know" or "knowledge" in Polish, depending on context.
In this sentence, 'wiedzą' functions as the noun 'wiedza' in its instrumental form, governed by the verb 'posiadają'.
Oni posiadają dużą wiedzę na ten temat.
They possess a lot of knowledge on this topic.
Here, 'wiedzą' is the third-person plural present tense of the verb 'wiedzieć,' meaning 'to know.'
Zachowują się, jakby wszystko wiedzieli.
They act as if they knew everything.
In this sentence, 'wiedzą' is part of the instrumental phrase to communicate 'their knowledge,' referring to the noun 'wiedza.'