IPA: /ɪmˈprɪzənmənt/
KK: /ɪmˈprɪzənmənt/
The state of being kept in a place, usually a prison, as a punishment for a crime.
The judge sentenced him to five years of imprisonment for his actions.
Imprisonment is formed from "in-" (meaning in or into), "prison" (from Old French *prison*, meaning a place of confinement), and "-ment" (meaning the action or result of). The word refers to the act or state of being confined within a prison.
Think of being 'in' ('in-') a 'place of confinement' ('prison') — that's what imprisonment means.