This is the 4060th most frequent Polish word.
agresywnego
The word "agresywnego" means "aggressive" (masculine singular genitive or accusative form) in English.
The word 'agresywnego' is an adjective in the genitive case, describing a masculine noun 'psa', which means 'dog'.
Widziałem agresywnego psa biegającego po parku.
I saw an aggressive dog running in the park.
Here 'agresywnym' takes the instrumental case, modifying 'tonie', which is a masculine noun referring to 'tone'.
Unikaj rozmawiania na ten temat w agresywnym tonie.
Avoid discussing this topic in an aggressive tone.
In this sentence, 'agresywnego' is in the genitive case, qualifying the masculine noun 'zachowania', which translates to 'behavior'.