Policial vs. polícia
In Portuguese, the distinction between the individual officer and the organization generally relies on the words policial and polícia. While referring to the institution is consistent, the word used for the individual person varies slightly depending on regional dialect (Brazil vs. Portugal) and context.
Policial
A1This is the most common noun used in Brazil to refer to the individual police officer. It works for both genders, distinguished only by the article (o policial for a male officer, a policial for a female officer).
O policial pediu os documentos do motorista.
(The police officer asked for the driver's documents.)
Ela decidiu ser policial para ajudar a comunidade.
(She decided to be a police officer to help the community.)
Os policiais chegaram rapidamente ao local.
(The policemen arrived quickly at the scene.)
A policial explicou as regras de segurança.
(The female police officer explained the safety rules.)
Polícia
A1Primarily, this word refers to the police force or institution as a collective group (a polícia). However, in European Portuguese (Portugal), o polícia is the standard term for a male policeman. In Brazil, it is sometimes used colloquially to address an officer directly.
A polícia está investigando o crime.
(The police are investigating the crime.)
O polícia prendeu o ladrão.
(The policeman arrested the thief (Common usage in Portugal).)
Alguém chame a polícia imediatamente.
(Someone call the police immediately.)
Bom dia, seu polícia, como vai?
(Good morning, officer, how are you? (Colloquial Brazilian usage).)
Summary
Use policial when referring to a specific individual officer, especially in Brazilian Portuguese (e.g., o policial). Use polícia when referring to the institution or the police force as a whole (e.g., a polícia). Note that in Portugal, o polícia is commonly used for the individual male officer.