Other forms: loopholes
A loophole is the small gap in a rule that lets clever people slip around it. A tax loophole, close the loophole, exploit a loophole.
It is a gap that lets somebody comply with the letter of a rule while defeating its purpose, which is why closing loopholes is endless work — every new rule creates new ones. The original loophole was a narrow slit in a castle wall for shooting arrows through, and the metaphor of a small opening in something solid is exactly right.
1nounloopholeA gap in a rule that lets people avoid its purpose.
“Rich people used a loophole in the tax law to avoid paying millions.”
loophole is a gap in a rule.
The word joins an old loop, meaning a narrow opening or slit in a wall, to hole. The arrow slit came first and the legal gap is the metaphor.
From loupe + hole, from a gem source. by surface analysis, loop + hole. Compare Medieval Latin loupa and Middle Dutch lupen (“to watch”).
Etymology from Wiktionary, CC BY-SA