This is the 12th most frequent Turkish word.
büyük
"Big" or "large."
In this sentence, 'büyük' is used as an adjective to describe the size of the city, meaning 'large' or 'big'.
Bu şehir çok büyük.
This city is very large.
Here, 'büyük' is again an adjective but it describes the size of a table, emphasizing the purchase of a large one.
Büyük bir masa aldık.
We bought a large table.
'Büyük' in this sentence is used metaphorically to indicate 'big' in terms of ambition or mindset, suggesting a way of thinking expansively.