A somewhat formal or bureaucratic term for a police officer, often used in legal or administrative contexts. The cross-reference 警察吏員 is a more explicit compound with the same meaning.
See also: 警察吏員
The police officer rushed to the scene.
Police officers at that time had more limited authority than today's police.
Compound of 警 (けい, 'warn, police') and 吏 (り, 'official, officer'). The exact historical derivation is uncertain, but it follows a common pattern for official titles.