IPA: /ˈprɪzənər/
KK: /ˈprɪzənər/
A person who is kept in a place like a jail or prison, usually because they have been accused of a crime or are serving a sentence.
The prisoner was released after serving ten years for his crime.
Prisoner → It is formed from "prison" (from Old French *prison*, meaning a place of confinement) and "-er" (meaning a person who). A prisoner is a person who is confined in a place of imprisonment.
Think of someone who is in a 'place of confinement' ('prison') — the '-er' just means a person. This helps you remember that a prisoner is someone who is confined.