From Middle English 'loupe' (narrow slit in a castle wall for shooting arrows) — a small gap in defenses that could be exploited.
An ambiguity or inadequacy in the law or a set of rules that can be exploited.
From Middle English 'loupe' (narrow opening) + 'hole.' Originally a narrow vertical slit in a castle wall through which defenders could shoot arrows while remaining protected. The idea of 'a small opening you can exploit' transferred from military architecture to legal language. Key