noun
policeman, police officer
B1
Polizist means 'policeman' or 'police officer'. It's a masculine noun (der Polizist) with plural Polizisten; it's a weak noun (n‑declension), so many oblique cases end in -en (des/dem/den Polizisten). Feminine form is Polizistin. No special prepositions or irregularities beyond the weak declension.
Examples
Die Zeugen beschrieben den Polizisten, dem sie die Wegbeschreibung gegeben hatten, und die Polizei bedankte sich später.
The witnesses described the policeman to whom they had given the directions, and the police thanked them later.
Der Polizist hat den Verkehr geregelt.
The policeman directed the traffic.
Der Polizist ist ein erfahrener Beamter in der Polizeidienststelle.
The police officer is an experienced official at the police station.
Details
Mnemonics
Picture a uniformed officer directing traffic to remember Polizist.
Polizist sounds like 'police' + '-ist'.
der (masculine) — many traditional job titles for men take 'der' (der Polizist).
Notes
Polizist is commonly used for male officers; Polizistin is the feminine form. Plural is Polizisten; note the weak declension pattern in the singular genitive/dative.