The castle was used as a jail.这城堡曾用作监狱。
The police put the escaped criminals back in jail.警方把越狱的罪犯押回监狱。

下面两句中定冠词的有无使句子的意思不同:
He worked in the jail.
他在监狱工作。
The police worked in jail.
警方把他收监。

jail还可用作动词表示“监禁,拘留”。例如:
He was jailed for life for murder.他因杀人罪被终身监禁。

［同义词］   prison
［词源］＜古法语jaiole(笼子,监牢)