the characterzh
囚
人
person
囗
enclosure
a person boxed in
Prisoner: a person (人) inside four walls (囗). Shuowen: 从人在囗中 — ‘a person within an enclosure’. You read it before you're taught it; the picture is the meaning.
source · 囚, a 會意 character; Shuowen: 囚，繫也，从人在囗中 — Wiktionary / 說文解字