secret passage; underground passage; escape tunnel
A hidden or secret passage, often underground, used for escape or covert movement.
The castle had a secret passage that allowed one to get outside without being noticed by the enemy.
loophole; gap in the rules
A figurative gap or flaw in a system, law, or argument that allows one to circumvent restrictions.
This law has many loopholes and may be exploited.
Standard spelling; the most common written form.
Abbreviated spelling; less common but still encountered.
Compound of 抜け (nuke, 'escaping' or 'passing through') and 穴 (ana, 'hole'). The figurative sense of 'loophole' developed from the literal idea of a hidden passage.