This is the 5538th most frequent Russian word.
полицейским
"Полицейским" translates to "policeman" or "police officer" in English.
In this sentence, 'полицейским' is used as an instrumental case noun describing one's occupation.
Я горжусь своим трудом полицейским.
I am proud of my work as a policeman.
Here, 'полицейским' is used in the dative case to indicate the recipient of something needed.
Полицейским требуется доказательство для расследования.
Police officers need evidence for the investigation.
In this case, 'полицейского' is used in the accusative case to denote the object of the verb.