牢 - prison, jail, hardness

imprisonment

prison; jail; gaol

dungeon; underground prison

precinct of a jail; vicinity of a prison

jail for women (Edo period)

life imprisonment

dungeon

firm and solid; stout and durable

prison; jail; gaol

firmly; strongly

keeping in mind; taking note of; remembering; taking to heart

locking the barn door after the horse has bolted; doing something too late; mending the pen after the sheep are lost